Although elements like <div>s normally grow to fit their contents, using the float property can cause a startling problem for CSS newbies: If floated elements have non-floated parent elements, the parent will collapse.
For example:
<div>
<div style="float: left;">Div 1</div>
<div style="float: left;">Div 2</div>
</div>The parent div in this example will not expand to contain its floated children - it will appear to have height: 0.
How do you solve this problem?
I would like to create an exhaustive list of solutions here. If you're aware of cross-browser compatibility issues, please point them out.
Solution 1
Float the parent.
<div style="float: left;">
<div style="float: left;">Div 1</div>
<div style="float: left;">Div 2</div>
</div>Pros: Semantic code.
Cons: You may not always want the parent floated. Even if you do, do you float the parents' parent, and so on? Must you float every ancestor element?
Solution 2
Give the parent an explicit height.
4 Answers
I usually use the overflow: auto trick; although that's not, strictly speaking, the intended use for overflow, it is kinda related - enough to make it easy to remember, certainly. The meaning of float: left itself has been extended for various uses more significantly than overflow is in this example, IMO.
The ideal solution would be to use inline-block for the columns instead of floating. I think the browser support is pretty good if you follow (a) apply inline-block only to elements that are normally inline (eg span); and (b) add -moz-inline-box for Firefox.
Check your page in FF2 as well because I had a ton of problems when nesting certain elements (surprisingly, this is the one case where IE performs much better than FF).
Another possible solution which I think is more semantically correct is to change the floated inner elements to be 'display: inline'. This example and what I was working on when I came across this page both use floated divs in much exactly the same way that a span would be used. Instead of using divs, switch to span, or if you are using another element which is by default 'display: block' instead of 'display: inline' then change it to be 'display: inline'. I believe this is the 100% semantically correct solution.
Solution 1, floating the parent, is essentially to change the entire document to be floated.
Solution 2, setting an explicit height, is like drawing a box and saying I want to put a picture here, i.e. use this if you are doing an img tag.
Solution 3, adding a spacer to clear float, is like adding an extra line below your content and will mess with surrounding elements too. If you use this approach you probably want to set the div to be height: 0px.
Solution 4, overflow: auto, is acknowledging that you don't know how to lay out the document and you are admitting that you don't know what to do.
I believe that best way is to set clear:both to the upcoming element.
Here's why:
1) :after selector is not supported in IE6/7 and buggy in FF3, however,
if you care only about IE8+ and FF3.5+ clearing with :after is probably best for you...
2) overflow is supposed to do something else so this hack isn't reliable enough.
Note to author: there is nothing hacky on clearing... Clearing means to skip the floating fields. CLEAR is with us since HTML3 (who knows, maybe even longer) http://www.w3.org/MarkUp/html3/deflists.html , maybe they should chose a bit different name like page: new, but thats just a detail...