CSS enables us to define many many rules for fonts, colors, sizes, positions, opacity, etc.
If you look for a specific rule, a good entry point is the w3school website.
In the following, we will see some basic rules so you can play with CSS.
text-align: center; (or left, right, ...)
text-decoration: none; (or underline, overline, ...)
text-transform: uppercase; (or lowercase, smallcaps, ...)
font-style: normal; (or italic, oblique, ...)
background-color: blue;
background-image: url("picture.png");
list-style-type: circle;
list-style-type: square;
list-style-type: upper-roman;
list-style-type: lower-alpha;
border-style: solid; (or dotted, ...)
border-top-style: dotted;
border-width: 5px; (or medium, ...)
border-width: 2px 10px 4px 20px;
border-color: red;
border-radius: 5px;