1) CSS Rule Structure

Web page styling rules are defined inline, embedded, or in an external .CSS file

Declarations grouped within a block:

selector {
     property: value;
     property: value;
     }

Element selector:
ul { padding-left: 5em; }

Selectors grouped within a rule:
ol, ul { margin-left: 5em; }

Class selector:
.entry-content { background-color: #c0c; }

Combination of element and class:
span.warning { font-weight: bold; }

ID selector:
#blog_title { font-size: 17px; }

Element within a class:

 .entry-content ol {
     background-color: #cc0;
     padding-left: 5em;
     }

Group combination & comment:
ol, ul { margin: 16px 0; padding: 0 0 0 40px; } /* top, right, bottom, left */

Inline syle:
<div style=”font-weight:bold; color:red”>Content</div>

Mind Blowing Declaration:

.entry-footer > span:not(:last-child):after {
     content: "\002f";
     display: inline-block;
     opacity: 0.7;
     padding: 0 0.538461538em;
     }