Thread:Project:Support desk/What is the server directory/file that holds the HTML/CSS code for the website?/reply

The HTML of the page is generated dynamically, the basic construct of the page is called the skin which you can find in skins/{skinname}/. There should be a Template which you can edit and change like you want.

The CSS is normally not centralized, so that special css rules can come from MediaWiki core, from the skin and others come maybe from extensions. They will be merged into one (better less) big css files and delivered by the ResourceLoader to the client. To change a css element of the skin you can look into the skin folder and find the less/css directory and change your things there. An alternative can be the MediaWiki:Common.css on-wiki page; the css code will load on every pageload.

For more information you can read Manual:Skinning.

If you give further information about what you want to change, maybe we can help better :)