[css] How do I prevent CSS inheritance?

I have a hierarchical navigation menu in my sidebar that uses nested lists (<ul> and <li> tags). I am using a pre-made theme that already has styles for list items, but I want to alter the style for the top-level items but NOT have it apply to the sub-items. Is there an easy way to apply styles to the top-level list item tag WITHOUT having those styles cascade down to its children list items? I understand that I can explicitly add overriding styles to the sub-items but I'd really like to avoid having to duplicate all of that style code if there is an easy way to just say "apply these styles to this class and DO NOT cascade them down to any children elements". Here is the html I'm using:

<ul id="sidebar">
  <li class="top-level-nav">
    <span>HEADING 1</span>
    <ul>
      <li>sub-heading A</li>
      <li>sub-heading B</li>
    </ul>
  </li>
  <li class="top-level-nav">
    <span>HEADING 2</span>
    <ul>
      <li>sub-heading A</li>
      <li>sub-heading B</li>
    </ul>
  </li>
</ul>

So the CSS has styles for #sidebar ul and #sidebar ul li already, but I'd like to add additional styles to #sidebar .top-level-nav that do NOT cascade down to its sub-children. Is there any way to do this simply or do I need to rearrange all of the styles so the styles that were on #sidebar ul are now specific to certain classes?

For example if you have two div in XHTML document.

<div id='div1'>
    <p>hello, how are you?</p>
    <div id='div2'>
        <p>I am fine, thank you.</p>
    </div>
</div>

Then try this in CSS.

#div1 > #div2 > p{
    color: red;
}

affect only 'div2' paragraph.

#div1 > p {
    color: red;
} 

affect only 'div1' paragraph.

just set them back to their defaults in the "#sidebar ul li" selector

Short answer is: No, it's not possible to prevent CSS inheritance. You can only override the styles that are set on the parents. See the spec:

Every element in an HTML document will inherit all inheritable properties from its parent except the root element (html), which doesn’t have a parent. -W3C

Apart from overriding every single inherited property. You can also use initial keyword, e.g. color: initial;. It also can be used together with all, e.g. all: initial;, that will reset all properties at once. Example:

.container {_x000D_
  color: blue;_x000D_
  font-style: italic;_x000D_
}_x000D_
.initial {_x000D_
  all: initial;_x000D_
}

<div class="container">_x000D_
  The quick brown <span class="initial">fox</span> jumps over the lazy dog_x000D_
</div>

Browser support tables according to Can I use...

• all (Currently no support in both IE and Edge, others are good)
• initial (Currently no support in IE, others are good)

You may find it useful by using direct children selector > in some cases. Example:

.list > li {_x000D_
  border: 1px solid red;_x000D_
  color: blue;_x000D_
}

<ul class="list">_x000D_
  <li>_x000D_
    <span>HEADING 1</span>_x000D_
    <ul>_x000D_
      <li>sub-heading A</li>_x000D_
      <li>sub-heading B</li>_x000D_
    </ul>_x000D_
  </li>_x000D_
  <li>_x000D_
    <span>HEADING 2</span>_x000D_
    <ul>_x000D_
      <li>sub-heading A</li>_x000D_
      <li>sub-heading B</li>_x000D_
    </ul>_x000D_
  </li>_x000D_
</ul>

The border style has been applied only to the direct children <li>s, as border is an non-inherited property. But text color has been applied to all the children, as color is an inherited property.

Therefore, > selector would be only useful with non-inherited properties, when it comes to preventing inheritance.

You can use the * selector to change the child styles back to the default

example

#parent {
    white-space: pre-wrap;
}

#parent * {
    white-space: initial;
}

You don't need the class reference for the lis. Instead of having CSS like

li.top-level-nav { color:black; }

you can write

ul#sidebar > li { color:black; }

This will apply the styling only to lis that immediately descend from the sidebar ul.

Wrapping with iframe makes parent css obsolete.

You either use the child selector

So using

#parent > child

Will make only the first level children to have the styles applied. Unfortunately IE6 doesn't support the child selector.

Otherwise you can use

#parent child child

To set another specific styles to children that are more than one level below.

You could use something like jQuery to "disable" this behaviour, though I hardly think it's a good solution as you get display logic in css & javascript. Still, depending upon your requirements you might find jQuery's css utils make life easier for you than trying hacky css, especially if you're trying to make it work for IE6

There is a property called all in the CSS3 inheritance module. It works like this:

#sidebar ul li {
  all: initial;
}

As of 2016-12, all browsers but IE/Edge and Opera Mini support this property.