Docs: replace CSS by utilities in examples (#35699)

* Drop .opacity-50 and .opacity-75 redefinition in examples

* Drop unused .card-img-right from blog example CSS files

* Use line-height utilities when possible

* Use rounded-* utilities in examples

* Replace .nav-underline by .nav-scroller and use it in examples.html default

* Use .mb-1 for .blog-post-title

* Remove unused CSS rule and use .fw-* utilities for carousels examples

* Use utilities for cheatsheet examples

* Extract some CSS to utilities for .nav-masthead .nav-link in cover example

* Dashboard group of minor modifications

* Dropdowns example: refactoring

* Dropdowns example refactoring: fix linting by removing selector by id

* Features example refactoring

* Headers example refactoring

* List groups example refactoring

* Sidebars example refactoring

* Sign-in example refactoring

* Starter template refactoring

* Fix RTL examples

Co-authored-by: Mark Otto <markd.otto@gmail.com>

site/content/docs/5.1/examples/dropdowns/dropdowns.css

@@ -1,20 +1,7 @@
 .dropdown-menu {
-  position: static;
-  display: block;
-  width: auto;
   margin: 4rem auto;
 }
 
-.dropdown-menu-macos {
-  display: grid;
-  gap: .25rem;
-  padding: .5rem;
-  border-radius: .5rem;
-}
-.dropdown-menu-macos .dropdown-item {
-  border-radius: .25rem;
-}
-
 .dropdown-item-danger {
   color: var(--bs-red);
 }
@@ -28,9 +15,7 @@
 }
 
 .btn-hover-light {
-  text-align: left;
   background-color: var(--bs-white);
-  border-radius: .25rem;
 }
 .btn-hover-light:hover,
 .btn-hover-light:focus {
@@ -74,3 +59,20 @@
   background-color: rgba(255, 255, 255, .05);
   border-color: rgba(255, 255, 255, .15);
 }
+
+
+.w-220px {
+  width: 220px;
+}
+
+.w-280px {
+  width: 280px;
+}
+
+.w-340px {
+  width: 340px;
+}
+
+.w-600px {
+  width: 600px;
+}