CSS: Guidelines for good CSS, heavily based on idiomatic.css.

idiomatic.css

/* ==========================================================================
   Section comment block
   ========================================================================== */

/* Sub-section comment block
   ========================================================================== */

/**
 * Short description using Doxygen-style comment format
 *
 * The first sentence of the long description starts here and continues on this
 * line for a while finally concluding here at the end of this paragraph.
 *
 * The long description is ideal for more detailed explanations and
 * documentation. It can include example HTML, URLs, or any other information
 * that is deemed necessary or useful.
 *
 * @tag This is a tag named 'tag'
 *
 * TODO: This is a todo statement that describes an atomic task to be completed
 * at a later date. It wraps after 80 characters and following lines are
 * indented by 2 spaces.
 */

/* Basic comment */

.selector {
   /* Positioning */
   position: absolute;
   z-index: 10;
   top: 0;
   right: 0;
   bottom: 0;
   left: 0;

   /* Display & Box Model */
   float: left;
   clear: left;
   display: inline-block;
   vertical-align: top;
   overflow: hidden;
   width: 100px;
   height: 100px;
   padding: 10px;
   margin: 10px;
   border: 10px solid #333;

   /* Color */
   color: #fff;
   background: #000;

   /* Text */
   font-family: sans-serif;
   font-size: 16px;
   line-height: 1.4;
   text-align: right;

   /* Misc */
   cursor: pointer;
   opacity: 1;
   visibility: visible;
}