javascript - CSS: Select element only if a later sibling exists

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javascript - CSS: Select element only if a later sibling exists

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

In my HTML structure, I have it set up like this:

<body>
   <main>
      <section>
      ...
      </section>

      <aside>
      ...
      </aside>
   </main>
</body>

The problem is, not all pages have <aside>

I need to select <section> and give it a max-width: 500px; ONLY when <aside> is present. The default is section { max-width: 1000px; } (when <aside> is absent)

Unlike in Selector for one tag directly followed by another tag; the user [asking the question] wants to style "B" ALL the time. Also, in this question, the user wants to select "B" (not "A")

I need to style <section> ONLY if <aside> is present.
I can't change the order of the HTML >_<
Can it be done with CSS only?
What selector do I need or how to set it up?
If it can't be done with CSS (I rather it be CSS-only), how can I accomplish this?

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1 Answer

深蓝 · Answer 1 · 2021-10-23T17:55:47+0000

A neat little trick

You can achieve what you want by using a trick to check if the <section> element is the only element in <main>. This will not work, if there are any other elements there. In your case it should work like this (http://jsfiddle.net/Ljm323qb/2/):

section {
     max-width: 500px;
}
/* The STAR of the show */
section:only-child {
     max-width: 1000px;
}

As illustrated in this codepen: http://codepen.io/omarjuvera/pen/ByXGyK?editors=110

General stuff on Sibling Selectors

There's the + selector which would select a sibling that comes right after the element (https://developer.mozilla.org/en-US/docs/Web/CSS/Adjacent_sibling_selectors)

And there's the ~ selector which selects all following siblings (https://developer.mozilla.org/en-US/docs/Web/CSS/General_sibling_selectors)

You could achieve it by putting the <aside> element before the <section> element and using a sibling selector.

Here's an example: http://jsfiddle.net/Ljm323qb/1/

A quick look in the future
Soon this will be possible, with a new :has pseudo class (http://dev.w3.org/csswg/selectors-4/#relational)
You'll be able to call something like main:has(> aside) > section { ... } but we'll have to wait for that, unfortunately :(

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javascript - CSS: Select element only if a later sibling exists

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1 Answer

A neat little trick

General stuff on Sibling Selectors

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