<p>The reasons are varied. Some add functionality, some add cosmetic changes. They have to be applies to the .css Mediawiki pages. </p><p>Have you read the Help page and explored the Dev Wiki for some ideas and tutorials? </p><p>It takes skill and knowledge to write css. If you’re a novice, it’s best to just copy existing code that you like. </p>

<p>I do know CSS, the problem would be finding a use for it, I'll check out those pages thanks </p>

<p>To make pages and wiki look nicer as a whole. You'll run into it eventually; when everything else is finished, you'll want to spice it up even more. That's when CSS comes to stage. </p><p>Also, it is hard to answer what particularly you can do with CSS. Just open some wikis as an example. You'll notice that certain elements do not look or function as they should be. </p>

<p>HTML tells you the bare minimum of what something is; CSS describes its visual appearance. For example, HTML would say you have a div element. CSS says that div element has a 2-pixel-wide red dashed border, 5-pixel-radius rounded corners, a height of 25 pixels, and a background that changes from red to yellow as you go from left to right. </p>