Notes on CSS floats
From http://www.simplebits.com/ April 3rd 2003 entry:
Not long after I updated my CSS, a reader pointed out that when resizing text, the content column would “jump” to the right, overlapping the sidebar. Not good.
The problem: I needed to clear the floats that enable the navigation to be horizontal. This didn’t seem to be a problem in my old, positioned layout. But when floats are used to lay out the columns that follow the navigation, not clearing can cause bizarre issues.
The solution: Adding a simple clear: left; to the #content declaration (since this
follows the navigation) solved the text resizing issue.
Something to keep in mind if you’re using a floating layout, along with an unordered navigation list that also uses float.
So… clear, clear, clear.