Help:Advanced formatting of wiki pages
CSS (Cascading Style Sheets) and JavaScript are generally involved in MediaWiki-based wikis. But while inline CSS is permitted, inline JavaScript is not available.
Most HTML tags, for example tt, code, pre, div, span, etc., can be directly embedded in the wiki markup; some HTML tags (for example a or img) cannot. For the allowed tags, you can define inline CSS by setting the style attribute, for instance <span style="border: 1px solid grey; padding: 0 1em">framed sometext</span>, which is rendered like this: framed sometext.
User-defined CSS and JavaScript are enabled on the Xenharmonic Wiki. If your personal solutions turn out to be useful for the overall wiki, they might be integrated into the site-wide styles or scripts.
Use the SandBox for experimentation or start a page in the user namespace, in other words as a subpage of your user page, for example User:YourName/Sandbox.