Apply style to element, only if a certain element exists next to it

Question

I\'m using the

tag on several pages, but on ONE page I\'m using an

tag that is preceded by the

<

Answer 1

This only works if the <section/> comes after the <aside/>:

<aside>content</aside>
<!-- if there is another node in between, use the '~' selector -->
<section>content</section>

In that case you could use aside ~ section or aside + section:

section {
    padding: 8px;
}
aside + section {
    width: 500px;
    float: left;
}

In all other cases you'll have to use JavaScript because these selectors only work in one direction, top to bottom.

With CSS4 there might be a way using the Subject of a selector with Child combinator, but that's future. This selector was removed from the specification.