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问题:

I am trying to change the background color of one list item while there is another background color for other list items.

This is what I have:

<style type="text/css">
    
ul.nav li
{
  display:inline;
  padding:1em;
  margin:1em;
  background-color:blue;
}
    
    
.selected
{
  background-color:red;
}

<ul class="nav">
 <li>Category 1</li>
 <li>Category 2</li>
 <li class="selected">Category 3</li>
 <li>Category 4</li>
</ul>

What this produces is all list items with a blue background (from the "nav" class), as if there were no "selected" class. However, when I take out the background color from the "nav" class, I get the red background for the list item with the "selected" class.

I would like to use the "selected" class for other items on the page (i.e. other list items, divs, etc.).

How would I go about solving this?

Thank you in advance.

回答1:

This is an issue of selector specificity. (The selector .selected is less specific than ul.nav li.)

To fix, use as much specificity in the overriding rule as in the original:

ul.nav li {
 background-color:blue;
}
ul.nav li.selected {
 background-color:red;
}

You might also consider nixing the ul, unless there will be other .navs. So:

.nav li {
 background-color:blue;
}
.nav li.selected {
 background-color:red;
}

That's a bit cleaner, less typing, and fewer bits.

回答2:

The ul.nav li is more restrictive and so takes precedence, try this:

ul.nav li.selected {  
  background-color:red; 
}

回答3:

Live Demo

If you want this to be highlighted depending upon the page your user is on then do this:

To auto-highlight your current navigation, first label your body tags with an ID or class that matches the section of the site (usually a directory) that the page is in.

<body class="ab">

We label all files in the "/about/" directory with the "ab" class. Note that we use a class here to label the body tags. We found that using an ID in the body did not work consistently in some older browsers. Next we label our menu items so we can target them individually thus:

<div id="n"> <a class="b" id="hm"
href="/">Home</a> ... <a class="b"
id="ab" href="/about/">About</a> ...
</div>

Note that we use the "b"utton class to label menu items as buttons and an ID ("ab") to label each unique menu item (in this case about). Now all we need is a CSS selector that matches up the body label with the appropriate menu label like this:

body.ab #n #ab, body.ab #n #ab
a{color:#333;background:#dcdcdc;text-decoration:none;}

This code effectively highlights the "About" menu item and makes it appear dark gray. When you label the rest of the site and menu items, you'll end up with a grouped selector that looks something like this:

body.hm #n #hm, body.hm #n #hm a,
body.sm #n #sm, body.sm #n #sm a,
body.is #n #is, body.is #n #is a,
body.ab #n #ab, body.ab #n #ab a, 
body.ct #n #ct, body.ct #n #ct
a{color:#333;background:#dcdcdc;text-decoration:none;}

For example when the user navigates to the sitemap section the .sm classed body tag matches the #sm menu option and triggers the CSS highlight of the "Sitemap" in the navigation bar.

Source

回答4:

Scenario: I have a navigation menu like this. Note: Link <a> is child of list item <li>. I wanted to change the background of the selected list item and remove the background color of unselected list item.

<nav>
        <ul>
            <li><a href="#">Intro</a></li>
            <li><a href="#">Size</a></li>
            <li><a href="#">Play</a></li>
            <li><a href="#">Food</a></li>
        </ul>
        <div class="clear"></div>

       </nav>

I tried to add a class .active into the list item using jQuery but it was not working

.active
{
    background-color: #480048;
}

$("nav li a").click(function () {
        $(this).parent().addClass("active");
        $(this).parent().siblings().removeClass("active");
    });

Solution: Basically, using .active class changing the background-color of list item does not work. So I changed the css class name from .active to "nav li.active a" so using the same javascript it will add the .active class into the selected list item. Now if the list item <li> has .active class then css will change the background color of the child of that list item <a>.

nav li.active a
{
    background-color: #480048;
}

回答5:

1) You can use the !important rule, like this:

.selected
{
  background-color:red !important;
}

See http://www.w3.org/TR/CSS2/cascade.html#important-rules for more info.

2) In your example you can also get the red background by using ul.nav li.selected instead of just .selected. This makes the selector more specific.

See http://www.w3.org/TR/CSS2/cascade.html#specificity for more info.