Board Thread:Support Requests - Getting Technical/@comment-3335785-20130220124714/@comment-4674838-20130220163026

If the CSS in question is meant to affect HTML elements which are normally part of a Wikia page (for example, the siderail or header -- as opposed to HTML elements which your script is dynamically creating like I said above), the only way to ensure that you don't see stuff "jump around" is to force your end users to @import your stylesheet like UltimateSupreme said.

Anytime you use JavaScript to load CSS, expect that there will be a delay between when you first see the page and when you first see your CSS take effect. Because JavaScript loads only after most HTML of the page has been parsed, per my comment about Resource Loader above.