add in a navbar button for toggling the nav items

less/bootstrap.less

@@ -33,6 +33,11 @@
 @import "component-animations.less";
 @import "close.less";
 
+// Components: Buttons & Alerts
+@import "buttons.less";
+@import "button-groups.less";
+@import "alerts.less"; // Note: alerts share common CSS with buttons and thus have styles in buttons.less
+
 // Components: Nav
 @import "navs.less";
 @import "navbar.less";
@@ -45,11 +50,6 @@
 @import "tooltip.less";
 @import "popovers.less";
 
-// Components: Buttons & Alerts
-@import "buttons.less";
-@import "button-groups.less";
-@import "alerts.less"; // Note: alerts share common CSS with buttons and thus have styles in buttons.less
-
 // Components: Misc
 @import "thumbnails.less";
 @import "labels.less";

less/navbar.less

@@ -16,6 +16,29 @@
   .box-shadow(@shadow);
 }
 
+// Navbar button for toggling navbar items in responsive layouts
+.btn-navbar {
+  display: none;
+  float: right;
+  padding: 7px 10px;
+  margin-left: 10px;
+  margin-right: 10px;
+  .buttonBackground(@navbarBackgroundHighlight, @navbarBackground);
+  @shadow: inset 0 1px 0 rgba(255,255,255,.1), 0 1px 0 rgba(255,255,255,.075);
+  .box-shadow(@shadow);
+}
+.btn-navbar .i-bar {
+  display: block;
+  width: 18px;
+  height: 2px;
+  background-color: #f5f5f5;
+  .border-radius(1px);
+  .box-shadow(0 1px 0 rgba(0,0,0,.25));
+}
+.btn-navbar .i-bar + .i-bar {
+  margin-top: 3px;
+}
+
 // Brand, links, text, and buttons
 .navbar {
   // Hover and active states

less/responsive.less

@@ -127,6 +127,11 @@
     margin: 0;
   }
 
+  // Navbar button
+  .btn-navbar {
+    display: block;
+  }
+
 }