diff --git a/packages/overlayscrollbars/src/autoUpdateLoop/autoUpdateLoop.ts b/packages/overlayscrollbars/src/autoUpdateLoop/autoUpdateLoop.ts
new file mode 100644
index 0000000..8e86797
--- /dev/null
+++ b/packages/overlayscrollbars/src/autoUpdateLoop/autoUpdateLoop.ts
@@ -0,0 +1,85 @@
+import { rAF, cAF, isEmptyArray, indexOf, createCache, runEach } from 'support';
+import { getEnvironment } from 'environment';
+
+export interface AutoUpdateLoop {
+  _add(fn: (delta: number) => any): () => void;
+  _interval(newInterval: number): () => void;
+  _interval(): number;
+}
+
+const defaultLoopInterval = 33;
+let autoUpdateLoopInstance: AutoUpdateLoop;
+
+const createAutoUpdateLoop = (): AutoUpdateLoop => {
+  let loopIsRunning = false;
+  let loopInterval = defaultLoopInterval;
+  let loopId: number | undefined;
+  const intervals: number[] = [];
+  const loopFunctions: Array<(...args: any) => any> = [];
+  const updateLoopInterval = () => {
+    loopInterval = isEmptyArray(intervals) ? defaultLoopInterval : Math.min.apply(null, intervals);
+  };
+  const updateTimeCache = createCache<number, number>((ctx) => ctx || performance.now(), {
+    _initialValue: performance.now(),
+    _equal: (currTime, newTime) => {
+      const delta = newTime! - currTime!;
+      return delta < loopInterval;
+    },
+  });
+  const loop = (newTime?: number) => {
+    /* istanbul ignore next */
+    if (!isEmptyArray(loopFunctions) && loopIsRunning) {
+      loopId = rAF!(loop);
+      const { _changed, _value, _previous } = updateTimeCache(0, newTime);
+      if (_changed) {
+        runEach(loopFunctions, _value! - _previous!);
+      }
+    }
+  };
+  function interval(): number;
+  function interval(newInterval: number): () => void;
+  function interval(newInterval?: number): number | (() => void) {
+    if (newInterval) {
+      intervals.push(newInterval);
+      updateLoopInterval();
+
+      return () => {
+        intervals.splice(indexOf(intervals, newInterval), 1);
+        updateLoopInterval();
+      };
+    }
+    return loopInterval;
+  }
+
+  return {
+    _add: (fn) => {
+      loopFunctions.push(fn);
+
+      if (!loopIsRunning && !isEmptyArray(loopFunctions)) {
+        getEnvironment()._autoUpdateLoop = loopIsRunning = true;
+
+        updateTimeCache(true);
+        loop();
+      }
+
+      return () => {
+        loopFunctions.splice(indexOf(loopFunctions, fn), 1);
+
+        if (isEmptyArray(loopFunctions) && loopIsRunning) {
+          getEnvironment()._autoUpdateLoop = loopIsRunning = false;
+
+          cAF!(loopId!);
+          loopId = undefined;
+        }
+      };
+    },
+    _interval: interval,
+  };
+};
+
+export const getAutoUpdateLoop = (): AutoUpdateLoop => {
+  if (!autoUpdateLoopInstance) {
+    autoUpdateLoopInstance = createAutoUpdateLoop();
+  }
+  return autoUpdateLoopInstance;
+};
diff --git a/packages/overlayscrollbars/src/autoUpdateLoop/index.ts b/packages/overlayscrollbars/src/autoUpdateLoop/index.ts
new file mode 100644
index 0000000..0dd1fa4
--- /dev/null
+++ b/packages/overlayscrollbars/src/autoUpdateLoop/index.ts
@@ -0,0 +1 @@
+export * from 'autoUpdateLoop/autoUpdateLoop';
diff --git a/packages/overlayscrollbars/src/classnames.ts b/packages/overlayscrollbars/src/classnames.ts
new file mode 100644
index 0000000..a196984
--- /dev/null
+++ b/packages/overlayscrollbars/src/classnames.ts
@@ -0,0 +1,18 @@
+export const classNameEnvironment = 'os-environment';
+export const classNameEnvironmentFlexboxGlue = `${classNameEnvironment}-flexbox-glue`;
+export const classNameEnvironmentFlexboxGlueMax = `${classNameEnvironmentFlexboxGlue}-max`;
+
+export const classNameHost = 'os-host';
+export const classNamePadding = 'os-padding';
+export const classNameViewport = 'os-viewport';
+export const classNameContent = 'os-content';
+export const classNameViewportScrollbarStyling = `${classNameViewport}-scrollbar-styled`;
+
+export const classNameSizeObserver = 'os-size-observer';
+export const classNameSizeObserverAppear = `${classNameSizeObserver}-appear`;
+export const classNameSizeObserverListener = `${classNameSizeObserver}-listener`;
+export const classNameSizeObserverListenerScroll = `${classNameSizeObserverListener}-scroll`;
+export const classNameSizeObserverListenerItem = `${classNameSizeObserverListener}-item`;
+export const classNameSizeObserverListenerItemFinal = `${classNameSizeObserverListenerItem}-final`;
+
+export const classNameTrinsicObserver = 'os-trinsic-observer';
diff --git a/packages/overlayscrollbars/src/environment/environment.ts b/packages/overlayscrollbars/src/environment/environment.ts
index 39cdd2f..89ca6a6 100644
--- a/packages/overlayscrollbars/src/environment/environment.ts
+++ b/packages/overlayscrollbars/src/environment/environment.ts
@@ -14,6 +14,12 @@ import {
   runEach,
   equalWH,
 } from 'support';
+import {
+  classNameEnvironment,
+  classNameEnvironmentFlexboxGlue,
+  classNameEnvironmentFlexboxGlueMax,
+  classNameViewportScrollbarStyling,
+} from 'classnames';
 
 export type OnEnvironmentChanged = (env: Environment) => void;
 export interface Environment {
@@ -29,9 +35,6 @@ export interface Environment {
 
 let environmentInstance: Environment;
 const { abs, round } = Math;
-const environmentElmId = 'os-environment';
-const classNameFlexboxGlue = 'flexbox-glue';
-const classNameFlexboxGlueMax = `${classNameFlexboxGlue}-max`;
 
 const getNativeScrollbarSize = (body: HTMLElement, measureElm: HTMLElement): XY => {
   appendChildren(body, measureElm);
@@ -46,7 +49,7 @@ const getNativeScrollbarSize = (body: HTMLElement, measureElm: HTMLElement): XY
 
 const getNativeScrollbarStyling = (testElm: HTMLElement): boolean => {
   let result = false;
-  addClass(testElm, 'os-viewport-scrollbar-styled');
+  addClass(testElm, classNameViewportScrollbarStyling);
   try {
     result =
       style(testElm, 'scrollbar-width') === 'none' || window.getComputedStyle(testElm, '::-webkit-scrollbar').getPropertyValue('display') === 'none';
@@ -83,12 +86,12 @@ const getRtlScrollBehavior = (parentElm: HTMLElement, childElm: HTMLElement): {
 };
 
 const getFlexboxGlue = (parentElm: HTMLElement, childElm: HTMLElement): boolean => {
-  addClass(parentElm, classNameFlexboxGlue);
+  addClass(parentElm, classNameEnvironmentFlexboxGlue);
   const minOffsetsizeParent = offsetSize(parentElm);
   const minOffsetsize = offsetSize(childElm);
   const supportsMin = equalWH(minOffsetsize, minOffsetsizeParent);
 
-  addClass(parentElm, classNameFlexboxGlueMax);
+  addClass(parentElm, classNameEnvironmentFlexboxGlueMax);
   const maxOffsetsizeParent = offsetSize(parentElm);
   const maxOffsetsize = offsetSize(childElm);
   const supportsMax = equalWH(maxOffsetsize, maxOffsetsizeParent);
@@ -114,7 +117,7 @@ const diffBiggerThanOne = (valOne: number, valTwo: number): boolean => {
 
 const createEnvironment = (): Environment => {
   const { body } = document;
-  const envDOM = createDOM(`<div id="${environmentElmId}"><div></div></div>`);
+  const envDOM = createDOM(`<div class="${classNameEnvironment}"><div></div></div>`);
   const envElm = envDOM[0] as HTMLElement;
   const envChildElm = envElm.firstChild as HTMLElement;
 
diff --git a/packages/overlayscrollbars/src/lifecycles/structureLifecycle.ts b/packages/overlayscrollbars/src/lifecycles/structureLifecycle.ts
index 16cecac..d05608f 100644
--- a/packages/overlayscrollbars/src/lifecycles/structureLifecycle.ts
+++ b/packages/overlayscrollbars/src/lifecycles/structureLifecycle.ts
@@ -5,11 +5,16 @@ import {
   createCache,
   topRightBottomLeft,
   TRBL,
+  WH,
+  XY,
   equalTRBL,
+  equalXY,
   optionsTemplateTypes as oTypes,
   OptionsTemplateValue,
   style,
   OptionsWithOptionsTemplate,
+  scrollSize,
+  offsetSize,
 } from 'support';
 import { OSTargetObject } from 'typings';
 import { createLifecycleBase, Lifecycle } from 'lifecycles/lifecycleBase';
@@ -33,11 +38,6 @@ const defaultOptionsWithTemplate: OptionsWithOptionsTemplate<Required<StructureL
   },
 };
 
-const classNameHost = 'os-host';
-const classNameViewport = 'os-viewport';
-const classNameContent = 'os-content';
-const classNameViewportScrollbarStyling = `${classNameViewport}-scrollbar-styled`;
-
 const cssMarginEnd = cssProperty('margin-inline-end');
 const cssBorderEnd = cssProperty('border-inline-end');
 
@@ -55,6 +55,13 @@ export const createStructureLifecycle = (
   const directionObserverObsolete = (cssMarginEnd && cssBorderEnd) || supportsScrollbarStyling || scrollbarsOverlaid.y;
 
   const updatePaddingCache = createCache(() => topRightBottomLeft(host, 'padding'), { _equal: equalTRBL });
+  const updateOverflowAmountCache = createCache<XY<number>, { _contentScrollSize: WH<number>; _viewportSize: WH<number> }>(
+    (ctx) => ({
+      x: Math.max(0, Math.round((ctx!._contentScrollSize.w - ctx!._viewportSize.w) * 100) / 100),
+      y: Math.max(0, Math.round((ctx!._contentScrollSize.h - ctx!._viewportSize.h) * 100) / 100),
+    }),
+    { _equal: equalXY }
+  );
 
   const { _options, _update } = createLifecycleBase<StructureLifecycleOptions>(defaultOptionsWithTemplate, initialOptions, (force, checkOption) => {
     const { _value: paddingAbsolute, _changed: paddingAbsoluteChanged } = checkOption('paddingAbsolute');
@@ -75,11 +82,6 @@ export const createStructureLifecycle = (
         paddingStyle.l = -padding!.l;
       }
 
-      if (!supportsScrollbarStyling) {
-        paddingStyle.r -= env._nativeScrollbarSize.y;
-        paddingStyle.b -= env._nativeScrollbarSize.x;
-      }
-
       style(paddingElm, {
         top: paddingStyle.t,
         left: paddingStyle.l,
@@ -88,6 +90,59 @@ export const createStructureLifecycle = (
         'max-width': `calc(100% + ${paddingStyle.r * -1}px)`,
       });
     }
+
+    const viewportOffsetSize = offsetSize(paddingElm);
+    const contentClientSize = offsetSize(content);
+    const contentScrollSize = scrollSize(content);
+    const overflowAmuntCache = updateOverflowAmountCache(force, {
+      _contentScrollSize: contentScrollSize,
+      _viewportSize: {
+        w: viewportOffsetSize.w + Math.max(0, contentClientSize.w - contentScrollSize.w),
+        h: viewportOffsetSize.h + Math.max(0, contentClientSize.h - contentScrollSize.h),
+      },
+    });
+    const { _value: overflowAmount, _changed: overflowAmountChanged } = overflowAmuntCache;
+
+    console.log('overflowAmount', overflowAmount);
+    console.log('overflowAmountChanged', overflowAmountChanged);
+
+    /*
+    var setOverflowVariables = function (horizontal) {
+      var scrollbarVars = getScrollbarVars(horizontal);
+      var scrollbarVarsInverted = getScrollbarVars(!horizontal);
+      var xyI = scrollbarVarsInverted._x_y;
+      var xy = scrollbarVars._x_y;
+      var wh = scrollbarVars._w_h;
+      var widthHeight = scrollbarVars._width_height;
+      var scrollMax = _strScroll + scrollbarVars._Left_Top + 'Max';
+      var fractionalOverflowAmount = viewportRect[widthHeight] ? MATH.abs(viewportRect[widthHeight] - _viewportSize[wh]) : 0;
+      var checkFractionalOverflowAmount = previousOverflowAmount && previousOverflowAmount[xy] > 0 && _viewportElementNative[scrollMax] === 0;
+      overflowBehaviorIsVS[xy] = overflowBehavior[xy] === 'v-s';
+      overflowBehaviorIsVH[xy] = overflowBehavior[xy] === 'v-h';
+      overflowBehaviorIsS[xy] = overflowBehavior[xy] === 's';
+      overflowAmount[xy] = MATH.max(0, MATH.round((contentScrollSize[wh] - _viewportSize[wh]) * 100) / 100);
+      overflowAmount[xy] *=
+        hideOverflowForceTextarea || (checkFractionalOverflowAmount && fractionalOverflowAmount > 0 && fractionalOverflowAmount < 1) ? 0 : 1;
+      hasOverflow[xy] = overflowAmount[xy] > 0;
+
+      //hideOverflow:
+      //x || y : true === overflow is hidden by "overflow: scroll" OR "overflow: hidden"
+      //xs || ys : true === overflow is hidden by "overflow: scroll"
+      hideOverflow[xy] =
+        overflowBehaviorIsVS[xy] || overflowBehaviorIsVH[xy]
+          ? hasOverflow[xyI] && !overflowBehaviorIsVS[xyI] && !overflowBehaviorIsVH[xyI]
+          : hasOverflow[xy];
+      hideOverflow[xy + 's'] = hideOverflow[xy] ? overflowBehaviorIsS[xy] || overflowBehaviorIsVS[xy] : false;
+
+      canScroll[xy] = hasOverflow[xy] && hideOverflow[xy + 's'];
+    };
+*/
+    /*
+    if (!supportsScrollbarStyling) {
+      paddingStyle.r -= env._nativeScrollbarSize.y;
+      paddingStyle.b -= env._nativeScrollbarSize.x;
+    }
+    */
   });
 
   const onSizeChanged = () => {
diff --git a/packages/overlayscrollbars/src/observers/domObserver.ts b/packages/overlayscrollbars/src/observers/domObserver.ts
new file mode 100644
index 0000000..748de7b
--- /dev/null
+++ b/packages/overlayscrollbars/src/observers/domObserver.ts
@@ -0,0 +1,89 @@
+import { each, indexOf, isString, MutationObserverConstructor, isEmptyArray, liesBetween } from 'support';
+import { classNameHost, classNameContent } from 'classnames';
+
+export interface DOMObserverOptions {
+  _observeContent?: boolean;
+  _attributes?: string[];
+}
+export interface DOMObserver {
+  _disconnect: () => void;
+  _update: () => void;
+}
+
+const styleChangingAttributes = ['id', 'class', 'style', 'open'];
+const mutationObserverAttrsTextarea = ['wrap', 'cols', 'rows'];
+
+const isUnknownMutation = (
+  attributeName: string | null,
+  type: MutationRecordType,
+  observeContent?: boolean,
+  target?: Node,
+  mutationTarget?: Node
+) => {
+  const isAttributesType = type === 'attributes';
+  const targetIsMutationTarget = target === mutationTarget;
+  const styleChangingAttrChanged = indexOf(styleChangingAttributes, attributeName) > -1;
+  const contentChanged = observeContent && !isAttributesType;
+  const contentAttrChanged =
+    observeContent &&
+    isAttributesType &&
+    styleChangingAttrChanged &&
+    !targetIsMutationTarget &&
+    !liesBetween(mutationTarget as Element | undefined, `.${classNameHost}`, `.${classNameContent}`);
+  const targetAttrChanged = isAttributesType && styleChangingAttrChanged && targetIsMutationTarget && !observeContent;
+
+  return contentChanged || contentAttrChanged || targetAttrChanged;
+};
+
+export const createDOMObserver = (
+  target: HTMLElement,
+  callback: (changedTargetAttrs: string[], styleChanged: boolean, contentChanged: boolean) => any,
+  options?: DOMObserverOptions
+): DOMObserver => {
+  const { _observeContent, _attributes } = options || {};
+
+  // MutationObserver
+  const observedAttributes = (_attributes || []).concat(_observeContent ? styleChangingAttributes : mutationObserverAttrsTextarea);
+  const observerCallback = (mutations: MutationRecord[]) => {
+    let styleChanged = false;
+    let contentChanged = false;
+    const changedTargetAttrs: string[] = [];
+    each(mutations, (mutation) => {
+      const { attributeName, target: mutationTarget, type } = mutation;
+
+      styleChanged = styleChanged || isUnknownMutation(attributeName, type);
+
+      if (_observeContent) {
+        contentChanged = contentChanged || isUnknownMutation(attributeName, type, true, target, mutationTarget);
+      }
+      if (isString(attributeName) && target === mutationTarget) {
+        changedTargetAttrs.push(attributeName);
+      }
+    });
+
+    if (!isEmptyArray(changedTargetAttrs) || styleChanged || contentChanged) {
+      callback(changedTargetAttrs, styleChanged, contentChanged);
+    }
+  };
+  const mutationObserver: MutationObserver = new MutationObserverConstructor!(observerCallback);
+
+  const connect = () => {
+    mutationObserver.observe(target, {
+      attributes: true,
+      attributeOldValue: true,
+      subtree: _observeContent,
+      childList: _observeContent,
+      characterData: _observeContent,
+      attributeFilter: observedAttributes,
+    });
+  };
+
+  connect();
+
+  return {
+    _disconnect: mutationObserver.disconnect,
+    _update: () => {
+      observerCallback(mutationObserver.takeRecords());
+    },
+  };
+};
diff --git a/packages/overlayscrollbars/src/observers/sizeObserver.ts b/packages/overlayscrollbars/src/observers/sizeObserver.ts
index 4ab4704..bcf6d97 100644
--- a/packages/overlayscrollbars/src/observers/sizeObserver.ts
+++ b/packages/overlayscrollbars/src/observers/sizeObserver.ts
@@ -17,22 +17,24 @@ import {
   addClass,
   isString,
   equalWH,
+  cAF,
+  rAF,
 } from 'support';
 import { CSSDirection } from 'typings';
 import { getEnvironment } from 'environment';
+import {
+  classNameSizeObserver,
+  classNameSizeObserverAppear,
+  classNameSizeObserverListener,
+  classNameSizeObserverListenerScroll,
+  classNameSizeObserverListenerItem,
+  classNameSizeObserverListenerItemFinal,
+} from 'classnames';
 
 const animationStartEventName = 'animationstart';
 const scrollEventName = 'scroll';
 const scrollAmount = 3333333;
 const ResizeObserverConstructor = jsAPI('ResizeObserver');
-const classNameSizeObserver = 'os-size-observer';
-const classNameSizeObserverAppear = `${classNameSizeObserver}-appear`;
-const classNameSizeObserverListener = `${classNameSizeObserver}-listener`;
-const classNameSizeObserverListenerScroll = `${classNameSizeObserverListener}-scroll`;
-const classNameSizeObserverListenerItem = `${classNameSizeObserverListener}-item`;
-const classNameSizeObserverListenerItemFinal = `${classNameSizeObserverListenerItem}-final`;
-const cAF = cancelAnimationFrame;
-const rAF = requestAnimationFrame;
 const getDirection = (elm: HTMLElement): CSSDirection => style(elm, 'direction') as CSSDirection;
 
 export type SizeObserverOptions = { _direction?: boolean; _appear?: boolean };
@@ -95,8 +97,8 @@ export const createSizeObserver = (
       isDirty = !scrollEvent || !equalWH(currSize, cacheSize);
 
       if (scrollEvent && isDirty && !rAFId) {
-        cAF(rAFId);
-        rAFId = rAF(onResized);
+        cAF!(rAFId);
+        rAFId = rAF!(onResized);
       } else if (!scrollEvent) {
         onResized();
       }
diff --git a/packages/overlayscrollbars/src/observers/trinsicObserver.ts b/packages/overlayscrollbars/src/observers/trinsicObserver.ts
index dad9482..354c764 100644
--- a/packages/overlayscrollbars/src/observers/trinsicObserver.ts
+++ b/packages/overlayscrollbars/src/observers/trinsicObserver.ts
@@ -1,8 +1,6 @@
-import { WH, Cache, createDOM, offsetSize, jsAPI, runEach, prependChildren, removeElements, createCache } from 'support';
+import { WH, Cache, createDOM, offsetSize, runEach, prependChildren, removeElements, createCache, IntersectionObserverConstructor } from 'support';
 import { createSizeObserver } from 'observers/sizeObserver';
-
-const classNameTrinsicObserver = 'os-trinsic-observer';
-const IntersectionObserverConstructor = jsAPI('IntersectionObserver');
+import { classNameTrinsicObserver } from 'classnames';
 
 export const createTrinsicObserver = (
   target: HTMLElement,
diff --git a/packages/overlayscrollbars/src/overlayscrollbars.scss b/packages/overlayscrollbars/src/overlayscrollbars.scss
index e871b93..26e238d 100644
--- a/packages/overlayscrollbars/src/overlayscrollbars.scss
+++ b/packages/overlayscrollbars/src/overlayscrollbars.scss
@@ -2,7 +2,7 @@
 @import './trinsicobserver.scss';
 @import './structurelifecycle.scss';
 
-#os-environment {
+.os-environment {
   position: fixed;
   opacity: 0;
   visibility: hidden;
@@ -16,7 +16,7 @@
     margin: 10px 0;
   }
 
-  &.flexbox-glue {
+  &.os-environment-flexbox-glue {
     display: flex;
     flex-direction: row;
     flex-wrap: nowrap;
@@ -35,7 +35,7 @@
     }
   }
 
-  &.flexbox-glue-max {
+  &.os-environment-flexbox-glue-max {
     max-height: 200px;
 
     div {
diff --git a/packages/overlayscrollbars/src/overlayscrollbars/OverlayScrollbars.ts b/packages/overlayscrollbars/src/overlayscrollbars/OverlayScrollbars.ts
index fed5871..61eab4f 100644
--- a/packages/overlayscrollbars/src/overlayscrollbars/OverlayScrollbars.ts
+++ b/packages/overlayscrollbars/src/overlayscrollbars/OverlayScrollbars.ts
@@ -4,11 +4,7 @@ import { Cache, appendChildren, addClass, contents, is, isHTMLElement, createDiv
 import { createSizeObserver } from 'observers/sizeObserver';
 import { createTrinsicObserver } from 'observers/trinsicObserver';
 import { Lifecycle } from 'lifecycles/lifecycleBase';
-
-const classNameHost = 'os-host';
-const classNamePadding = 'os-padding';
-const classNameViewport = 'os-viewport';
-const classNameContent = 'os-content';
+import { classNameHost, classNamePadding, classNameViewport, classNameContent } from 'classnames';
 
 const normalizeTarget = (target: OSTarget): OSTargetObject => {
   if (isHTMLElement(target)) {
diff --git a/packages/overlayscrollbars/src/support/cache/cache.ts b/packages/overlayscrollbars/src/support/cache/cache.ts
index ea52fc1..fa754c3 100644
--- a/packages/overlayscrollbars/src/support/cache/cache.ts
+++ b/packages/overlayscrollbars/src/support/cache/cache.ts
@@ -13,20 +13,20 @@ export type CacheUpdate<T, C> = (force?: boolean | 0, context?: C) => Cache<T>;
 
 export type UpdateCachePropFunction<T, C> = (context?: C, current?: T, previous?: T) => T;
 
-export type EqualCachePropFunction<T> = (a?: T, b?: T) => boolean;
+export type EqualCachePropFunction<T> = (currentVal?: T, newVal?: T) => boolean;
 
 export const createCache = <T, C = undefined>(update: UpdateCachePropFunction<T, C>, options?: CacheOptions<T>): CacheUpdate<T, C> => {
   const { _equal, _initialValue } = options || {};
   let _value: T | undefined = _initialValue;
   let _previous: T | undefined;
   return (force, context) => {
-    const prev = _value;
+    const curr = _value;
     const newVal = update(context, _value, _previous);
-    const changed = force || (_equal ? !_equal(prev, newVal) : prev !== newVal);
+    const changed = force || (_equal ? !_equal(curr, newVal) : curr !== newVal);
 
     if (changed) {
       _value = newVal;
-      _previous = prev;
+      _previous = curr;
     }
 
     return {
diff --git a/packages/overlayscrollbars/src/support/compatibility/apis.ts b/packages/overlayscrollbars/src/support/compatibility/apis.ts
index 3724de2..d080c88 100644
--- a/packages/overlayscrollbars/src/support/compatibility/apis.ts
+++ b/packages/overlayscrollbars/src/support/compatibility/apis.ts
@@ -1,3 +1,7 @@
 import { jsAPI } from 'support/compatibility/vendors';
 
-export const resizeObserver: any | undefined = jsAPI('ResizeObserver');
+export const MutationObserverConstructor = jsAPI<typeof MutationObserver>('MutationObserver');
+export const IntersectionObserverConstructor = jsAPI<typeof IntersectionObserver>('IntersectionObserver');
+export const ResizeObserverConstructor: any | undefined = jsAPI('ResizeObserver');
+export const cAF = jsAPI<typeof cancelAnimationFrame>('cancelAnimationFrame');
+export const rAF = jsAPI<typeof requestAnimationFrame>('requestAnimationFrame');
diff --git a/packages/overlayscrollbars/src/support/dom/dimensions.ts b/packages/overlayscrollbars/src/support/dom/dimensions.ts
index 5edb97a..9ae61f0 100644
--- a/packages/overlayscrollbars/src/support/dom/dimensions.ts
+++ b/packages/overlayscrollbars/src/support/dom/dimensions.ts
@@ -18,8 +18,8 @@ export const windowSize = (): WH => ({
 });
 
 /**
- * Returns the offset- width and height of the passed element. If the element is null the width and height values are 0.
- * @param elm The element of which the offset- width and height shall be returned.
+ * Returns the scroll- width and height of the passed element. If the element is null the width and height values are 0.
+ * @param elm The element of which the scroll- width and height shall be returned.
  */
 export const offsetSize = (elm: HTMLElement | null): WH =>
   elm
@@ -41,6 +41,18 @@ export const clientSize = (elm: HTMLElement | null): WH =>
       }
     : zeroObj;
 
+/**
+ * Returns the client- width and height of the passed element. If the element is null the width and height values are 0.
+ * @param elm The element of which the client- width and height shall be returned.
+ */
+export const scrollSize = (elm: HTMLElement | null): WH =>
+  elm
+    ? {
+        w: elm.scrollWidth,
+        h: elm.scrollHeight,
+      }
+    : zeroObj;
+
 /**
  * Returns the BoundingClientRect of the passed element.
  * @param elm The element of which the BoundingClientRect shall be returned.
diff --git a/packages/overlayscrollbars/src/support/dom/manipulation.ts b/packages/overlayscrollbars/src/support/dom/manipulation.ts
index fc8831f..db4fd39 100644
--- a/packages/overlayscrollbars/src/support/dom/manipulation.ts
+++ b/packages/overlayscrollbars/src/support/dom/manipulation.ts
@@ -69,7 +69,7 @@ export const prependChildren = (node: Node | null, children: NodeCollection): vo
  * @param insertedNodes The Nodes which shall be inserted.
  */
 export const insertBefore = (node: Node | null, insertedNodes: NodeCollection): void => {
-  before(parent(node), node, insertedNodes);
+  before(parent(node as Element), node, insertedNodes);
 };
 
 /**
@@ -78,7 +78,7 @@ export const insertBefore = (node: Node | null, insertedNodes: NodeCollection):
  * @param insertedNodes The Nodes which shall be inserted.
  */
 export const insertAfter = (node: Node | null, insertedNodes: NodeCollection): void => {
-  before(parent(node), node && node.nextSibling, insertedNodes);
+  before(parent(node as Element), node && node.nextSibling, insertedNodes);
 };
 
 /**
@@ -89,7 +89,7 @@ export const removeElements = (nodes: NodeCollection): void => {
   if (isArrayLike(nodes)) {
     each(from(nodes), (e) => removeElements(e));
   } else if (nodes) {
-    const parentElm = parent(nodes);
+    const parentElm = parent(nodes as Element);
     if (parentElm) {
       parentElm.removeChild(nodes);
     }
diff --git a/packages/overlayscrollbars/src/support/dom/traversal.ts b/packages/overlayscrollbars/src/support/dom/traversal.ts
index e53e0fd..a6f4fe0 100644
--- a/packages/overlayscrollbars/src/support/dom/traversal.ts
+++ b/packages/overlayscrollbars/src/support/dom/traversal.ts
@@ -1,22 +1,16 @@
 import { each, from } from 'support/utils/array';
 
-const matches = (elm: Element | null, selector: string): boolean => {
-  if (elm) {
-    /* istanbul ignore next */
-    // eslint-disable-next-line
-    // @ts-ignore
-    const fn = Element.prototype.matches || Element.prototype.msMatchesSelector;
-    return fn.call(elm, selector);
-  }
-  return false;
-};
+type InputElementType = Element | null | undefined;
+type OutputElementType = Element | null;
+
+const elmPrototype = Element.prototype;
 
 /**
  * Find all elements with the passed selector, outgoing (and including) the passed element or the document if no element was provided.
  * @param selector The selector which has to be searched by.
  * @param elm The element from which the search shall be outgoing.
  */
-export const find = (selector: string, elm?: Element | null): ReadonlyArray<Element> => {
+const find = (selector: string, elm?: InputElementType): ReadonlyArray<Element> => {
   const arr: Array<Element> = [];
 
   each((elm || document).querySelectorAll(selector), (e: Element) => {
@@ -31,26 +25,35 @@ export const find = (selector: string, elm?: Element | null): ReadonlyArray<Elem
  * @param selector The selector which has to be searched by.
  * @param elm The element from which the search shall be outgoing.
  */
-export const findFirst = (selector: string, elm?: Element | null): Element | null => (elm || document).querySelector(selector);
+const findFirst = (selector: string, elm?: InputElementType): OutputElementType => (elm || document).querySelector(selector);
 
 /**
  * Determines whether the passed element is matching with the passed selector.
  * @param elm The element which has to be compared with the passed selector.
  * @param selector The selector which has to be compared with the passed element. Additional selectors: ':visible' and ':hidden'.
  */
-export const is = (elm: Element | null, selector: string): boolean => matches(elm, selector);
+const is = (elm: InputElementType, selector: string): boolean => {
+  if (elm) {
+    /* istanbul ignore next */
+    // eslint-disable-next-line
+    // @ts-ignore
+    const fn = elmPrototype.matches || elmPrototype.msMatchesSelector;
+    return fn.call(elm, selector);
+  }
+  return false;
+};
 
 /**
  * Returns the children (no text-nodes or comments) of the passed element which are matching the passed selector. An empty array is returned if the passed element is null.
  * @param elm The element of which the children shall be returned.
  * @param selector The selector which must match with the children elements.
  */
-export const children = (elm: Element | null, selector?: string): ReadonlyArray<Element> => {
+const children = (elm: InputElementType, selector?: string): ReadonlyArray<Element> => {
   const childs: Array<Element> = [];
 
   each(elm && elm.children, (child: Element) => {
     if (selector) {
-      if (matches(child, selector)) {
+      if (is(child, selector)) {
         childs.push(child);
       }
     } else {
@@ -65,10 +68,47 @@ export const children = (elm: Element | null, selector?: string): ReadonlyArray<
  * Returns the childNodes (incl. text-nodes or comments etc.) of the passed element. An empty array is returned if the passed element is null.
  * @param elm The element of which the childNodes shall be returned.
  */
-export const contents = (elm: Element | null): ReadonlyArray<ChildNode> => (elm ? from(elm.childNodes) : []);
+const contents = (elm: InputElementType): ReadonlyArray<ChildNode> => (elm ? from(elm.childNodes) : []);
 
 /**
  * Returns the parent element of the passed element, or null if the passed element is null.
  * @param elm The element of which the parent element shall be returned.
  */
-export const parent = (elm: Node | null): Node | null => (elm ? elm.parentElement : null);
+const parent = (elm: InputElementType): OutputElementType => (elm ? elm.parentElement : null);
+
+const closest = (elm: InputElementType, selector: string): OutputElementType => {
+  if (elm) {
+    // eslint-disable-next-line
+    // @ts-ignore
+    if (elmPrototype.closest) {
+      return elm.closest(selector);
+    }
+    do {
+      if (is(elm, selector)) {
+        return elm;
+      }
+      elm = parent(elm);
+    } while (elm !== null && elm.nodeType === 1);
+  }
+
+  return null;
+};
+
+/**
+ * Determines whether the given element lies between two selectors in the DOM.
+ * @param elm The element.
+ * @param highBoundarySelector The high boundary selector.
+ * @param deepBoundarySelector The deep boundary selector.
+ */
+const liesBetween = (elm: InputElementType, highBoundarySelector: string, deepBoundarySelector: string): boolean => {
+  const closestHighBoundaryElm = closest(elm, highBoundarySelector);
+  const closestDeepBoundaryElm = findFirst(deepBoundarySelector, closestHighBoundaryElm);
+
+  return closestHighBoundaryElm && closestDeepBoundaryElm
+    ? closestHighBoundaryElm === elm ||
+        closestDeepBoundaryElm === elm ||
+        closest(closest(elm, deepBoundarySelector), highBoundarySelector) !== closestHighBoundaryElm
+    : false;
+};
+
+export { find, findFirst, is, children, contents, parent, liesBetween };
diff --git a/packages/overlayscrollbars/src/support/utils/array.ts b/packages/overlayscrollbars/src/support/utils/array.ts
index e592ca7..95021de 100644
--- a/packages/overlayscrollbars/src/support/utils/array.ts
+++ b/packages/overlayscrollbars/src/support/utils/array.ts
@@ -15,23 +15,26 @@ export function each<T>(
   callback: (value: T, indexOrKey: number, source: Array<T>) => boolean | void
 ): Array<T> | ReadonlyArray<T>;
 export function each<T>(
-  array: Array<T> | ReadonlyArray<T> | null,
+  array: Array<T> | ReadonlyArray<T> | null | undefined,
   callback: (value: T, indexOrKey: number, source: Array<T>) => boolean | void
-): Array<T> | ReadonlyArray<T> | null;
+): Array<T> | ReadonlyArray<T> | null | undefined;
 export function each<T>(
   arrayLikeObject: ArrayLike<T>,
   callback: (value: T, indexOrKey: number, source: ArrayLike<T>) => boolean | void
 ): ArrayLike<T>;
 export function each<T>(
-  arrayLikeObject: ArrayLike<T> | null,
+  arrayLikeObject: ArrayLike<T> | null | undefined,
   callback: (value: T, indexOrKey: number, source: ArrayLike<T>) => boolean | void
-): ArrayLike<T> | null;
+): ArrayLike<T> | null | undefined;
 export function each(obj: PlainObject, callback: (value: any, indexOrKey: string, source: PlainObject) => boolean | void): PlainObject;
-export function each(obj: PlainObject | null, callback: (value: any, indexOrKey: string, source: PlainObject) => boolean | void): PlainObject | null;
+export function each(
+  obj: PlainObject | null | undefined,
+  callback: (value: any, indexOrKey: string, source: PlainObject) => boolean | void
+): PlainObject | null | undefined;
 export function each<T>(
-  source: ArrayLike<T> | PlainObject | null,
+  source: ArrayLike<T> | PlainObject | null | undefined,
   callback: (value: T, indexOrKey: any, source: any) => boolean | void
-): Array<T> | ReadonlyArray<T> | ArrayLike<T> | PlainObject | null {
+): Array<T> | ReadonlyArray<T> | ArrayLike<T> | PlainObject | null | undefined {
   if (isArrayLike(source)) {
     for (let i = 0; i < source.length; i++) {
       if (callback(source[i], i, source) === false) {
@@ -67,14 +70,21 @@ export const from = <T = any>(arr: ArrayLike<T>) => {
   return result;
 };
 
+/**
+ * Check whether the passed array is empty.
+ * @param array The array which shall be checked.
+ */
+export const isEmptyArray = (array: Array<any> | null | undefined) => array && array.length === 0;
+
 /**
  * Calls all functions in the passed array/set of functions.
  * @param arr The array filled with function which shall be called.
+ * @param p1 The first param.
  */
-export const runEach = (arr: ArrayLike<RunEachItem> | Set<RunEachItem>): void => {
+export const runEach = (arr: ArrayLike<RunEachItem> | Set<RunEachItem>, p1?: unknown): void => {
   if (arr instanceof Set) {
-    arr.forEach((fn) => fn && fn());
+    arr.forEach((fn) => fn && fn(p1));
   } else {
-    each(arr, (fn) => fn && fn());
+    each(arr, (fn) => fn && fn(p1));
   }
 };
diff --git a/packages/overlayscrollbars/src/support/utils/index.ts b/packages/overlayscrollbars/src/support/utils/index.ts
index e80b708..787f33e 100644
--- a/packages/overlayscrollbars/src/support/utils/index.ts
+++ b/packages/overlayscrollbars/src/support/utils/index.ts
@@ -1,4 +1,5 @@
 export * from 'support/utils/array';
 export * from 'support/utils/equal';
+export * from 'support/utils/lexicon';
 export * from 'support/utils/object';
 export * from 'support/utils/types';
diff --git a/packages/overlayscrollbars/src/support/utils/lexicon.ts b/packages/overlayscrollbars/src/support/utils/lexicon.ts
new file mode 100644
index 0000000..27cefbc
--- /dev/null
+++ b/packages/overlayscrollbars/src/support/utils/lexicon.ts
@@ -0,0 +1,28 @@
+interface GenericLexicon<T extends boolean> {
+  _widthHeight: T extends true ? 'width' : 'height';
+  _WidthHeight: T extends true ? 'Width' : 'Height';
+  _leftTop: T extends true ? 'left' : 'top';
+  _LeftTop: T extends true ? 'Left' : 'Top';
+  _xy: T extends true ? 'x' : 'y';
+  _XY: T extends true ? 'X' : 'Y';
+  _wh: T extends true ? 'w' : 'h';
+  _lt: T extends true ? 'l' : 't';
+}
+
+export interface Lexicon<T extends boolean> extends GenericLexicon<T> {
+  _inverted: Lexicon<T extends true ? false : true>;
+}
+
+export const getLexicon = <T extends boolean = false>(horizontal?: T): Lexicon<T> => {
+  return {
+    _widthHeight: horizontal ? 'width' : 'height',
+    _WidthHeight: horizontal ? 'Width' : 'Height',
+    _leftTop: horizontal ? 'left' : 'top',
+    _LeftTop: horizontal ? 'Left' : 'Top',
+    _xy: horizontal ? 'x' : 'y',
+    _XY: horizontal ? 'X' : 'Y',
+    _wh: horizontal ? 'w' : 'h',
+    _lt: horizontal ? 'l' : 't',
+    _inverted: getLexicon(!horizontal),
+  } as Lexicon<T>;
+};
diff --git a/packages/overlayscrollbars/tests/jsdom/support/autoUpdateLoop/autoUpdateLoop.test.ts b/packages/overlayscrollbars/tests/jsdom/support/autoUpdateLoop/autoUpdateLoop.test.ts
new file mode 100644
index 0000000..0828654
--- /dev/null
+++ b/packages/overlayscrollbars/tests/jsdom/support/autoUpdateLoop/autoUpdateLoop.test.ts
@@ -0,0 +1,77 @@
+import { getAutoUpdateLoop } from 'autoUpdateLoop';
+import { getEnvironment } from 'environment';
+
+describe('autoUpdateLoop', () => {
+  test('first creation', async () => {
+    const deltas: number[] = [];
+    const wait = 2700;
+    const loop = getAutoUpdateLoop();
+    const defaultInterval = loop._interval();
+    await new Promise((resolve) => setTimeout(resolve, 1000));
+    const added = Date.now();
+    const remove = loop._add((delta) => {
+      if (deltas.length === 0) {
+        expect(Date.now() - added >= defaultInterval).toBe(true);
+      }
+      expect(delta >= defaultInterval).toBe(true);
+      deltas.push(delta);
+    });
+    expect(getEnvironment()._autoUpdateLoop).toBe(true);
+
+    await new Promise((resolve) => setTimeout(resolve, wait));
+    const elapsedDeltas = deltas.reduce((a, b) => a + b, 0);
+
+    expect(wait - elapsedDeltas < defaultInterval * 2).toBe(true);
+
+    remove();
+    expect(getEnvironment()._autoUpdateLoop).toBe(false);
+  });
+
+  test('add multiple', async () => {
+    const loop = getAutoUpdateLoop();
+    const fn1 = jest.fn();
+    const fn2 = jest.fn();
+    const fn3 = jest.fn();
+
+    const remove1 = loop._add(fn1);
+    const remove2 = loop._add(fn2);
+    const remove3 = loop._add(fn3);
+
+    expect(getEnvironment()._autoUpdateLoop).toBe(true);
+
+    await new Promise((resolve) => setTimeout(resolve, 2500));
+
+    expect(fn1).toHaveBeenCalledTimes(fn1.mock.calls.length);
+    expect(fn2).toHaveBeenCalledTimes(fn1.mock.calls.length);
+    expect(fn3).toHaveBeenCalledTimes(fn1.mock.calls.length);
+
+    remove1();
+    remove2();
+    remove3();
+
+    expect(getEnvironment()._autoUpdateLoop).toBe(false);
+  });
+
+  test('change interval', async () => {
+    const loop = getAutoUpdateLoop();
+    const defaultInterval = loop._interval();
+
+    const remove10 = loop._interval(10);
+    const remove5 = loop._interval(5);
+    const remove3 = loop._interval(3);
+    const remove8 = loop._interval(8);
+    const remove15 = loop._interval(15);
+
+    expect(loop._interval()).toBe(3);
+    remove3();
+    expect(loop._interval()).toBe(5);
+    remove10();
+    remove8();
+    expect(loop._interval()).toBe(5);
+    remove5();
+    expect(loop._interval()).toBe(15);
+    remove15();
+
+    expect(loop._interval()).toBe(defaultInterval);
+  });
+});
diff --git a/packages/overlayscrollbars/tests/jsdom/support/dom/dimensions.test.ts b/packages/overlayscrollbars/tests/jsdom/support/dom/dimensions.test.ts
index 7871a74..0786b36 100644
--- a/packages/overlayscrollbars/tests/jsdom/support/dom/dimensions.test.ts
+++ b/packages/overlayscrollbars/tests/jsdom/support/dom/dimensions.test.ts
@@ -1,6 +1,6 @@
 import { isNumber, isPlainObject } from 'support/utils/types';
 import { createDiv } from 'support/dom/create';
-import { windowSize, offsetSize, clientSize, getBoundingClientRect, hasDimensions } from 'support/dom/dimensions';
+import { windowSize, offsetSize, clientSize, scrollSize, getBoundingClientRect, hasDimensions } from 'support/dom/dimensions';
 
 describe('dom dimensions', () => {
   describe('offsetSize', () => {
@@ -35,6 +35,22 @@ describe('dom dimensions', () => {
     });
   });
 
+  describe('scrollSize', () => {
+    test('DOM element', () => {
+      const result = scrollSize(document.body);
+      expect(isPlainObject(result)).toBe(true);
+      expect(isNumber(result.w)).toBe(true);
+      expect(isNumber(result.h)).toBe(true);
+    });
+
+    test('null', () => {
+      const result = scrollSize(null);
+      expect(isPlainObject(result)).toBe(true);
+      expect(isNumber(result.w)).toBe(true);
+      expect(isNumber(result.h)).toBe(true);
+    });
+  });
+
   test('windowSize', () => {
     const result = windowSize();
     expect(isPlainObject(result)).toBe(true);
diff --git a/packages/overlayscrollbars/tests/jsdom/support/dom/traversal.test.ts b/packages/overlayscrollbars/tests/jsdom/support/dom/traversal.test.ts
index 2062c33..e5da87f 100644
--- a/packages/overlayscrollbars/tests/jsdom/support/dom/traversal.test.ts
+++ b/packages/overlayscrollbars/tests/jsdom/support/dom/traversal.test.ts
@@ -1,4 +1,4 @@
-import { find, findFirst, is, children, contents, parent, createDiv } from 'support/dom';
+import { find, findFirst, is, children, contents, parent, createDiv, liesBetween } from 'support/dom';
 
 const slotElm = document.body;
 const testHTML = '<div id="parent" class="div-class"><div id="child" class="div-class"></div></div><p>2</p><input type="text" value="3"></input>abc';
@@ -199,4 +199,92 @@ describe('dom traversal', () => {
       expect(p).toBeNull();
     });
   });
+
+  describe('liesBetween', () => {
+    const elmsBetween = ['.host', '.something', '.something-a', '.something-b', '.padding', '.viewport', '.content'];
+    const elmsOutside = ['.allowed-a', '.allowed-b', '.allowed-c', '.deeper-a', '.deeper-b'];
+    const elmsToTest = [...elmsBetween, ...elmsOutside];
+    const domPart = (id: string, content?: string) => `
+      <div id="${id}" class="host">
+        <div class="something">
+          <div class="something-a">
+            <div class="something-b">
+            </div>
+          </div>
+        </div>
+        <div class="padding">
+          <div class="viewport">
+            <div class="content">
+              <div class="allowed-a"><div class="allowed-b"><div class="allowed-c"></div></div></div>
+              <div class="deeper-a"><div class="deeper-b">${content || ''}</div></div>
+            </div>
+          </div>
+        </div>
+      </div>
+      `;
+    const createTestDOM = (nestings = 0) => {
+      let part = '';
+      for (let i = 0; i < nestings + 1; i++) {
+        part = domPart(`host-${nestings - i}`, part);
+      }
+
+      return part;
+    };
+    const genericTest = (nestings: number) => {
+      const allHostIds = Array(nestings)
+        .fill(0)
+        .map((_, index) => `#host-${index}`);
+
+      const test = (hostId: string, remainingIds: string[]) => {
+        const runExpectance = (id: string) => {
+          const isRemainingId = remainingIds.includes(id);
+          elmsToTest.forEach((elm) => {
+            const hostElm = findFirst(`${id}`);
+            const searchElm = hostElm?.classList.contains(elm.substring(1)) ? hostElm : findFirst(`${id} ${elm}`);
+
+            expect(liesBetween(searchElm, `${hostId}`, '.content')).toBe(
+              isRemainingId ? false : elmsBetween.includes(elm) ? true : elmsOutside.includes(elm) ? false : undefined
+            );
+          });
+        };
+
+        runExpectance(hostId);
+
+        remainingIds.forEach((id) => {
+          runExpectance(id);
+        });
+      };
+
+      elmsBetween.forEach((elm) => {
+        expect(liesBetween(findFirst(elm), '.host', '.content')).toBe(true);
+      });
+
+      elmsOutside.forEach((elm) => {
+        expect(liesBetween(findFirst(elm), '.host', '.content')).toBe(false);
+      });
+
+      for (let i = 0; i < nestings; i++) {
+        const currHostId = allHostIds[i];
+        const remainingIds = allHostIds.filter((id) => id !== currHostId);
+
+        test(currHostId, remainingIds);
+      }
+    };
+
+    test('with native closest', () => {
+      slotElm.innerHTML = createTestDOM(3);
+      genericTest(3);
+    });
+
+    test('with polyfill closest', () => {
+      const original = Element.prototype.closest;
+      // @ts-ignore
+      Element.prototype.closest = undefined;
+
+      slotElm.innerHTML = createTestDOM(3);
+      genericTest(3);
+
+      Element.prototype.closest = original;
+    });
+  });
 });