How to reference nested classes with css?

问题

When using css, how can I specify a nested class.

Here is my html code:

<div class="box1">
    <div class="box box-default">
      <div class="box-header with-border">
        <h3 class="box-title">Collapsable</h3>
        <div class="box-tools pull-right">
          <button class="btn btn-box-tool" data-widget="collapse"><i class="fa fa-minus"></i></button>
        </div><!-- /.box-tools -->
      </div><!-- /.box-header -->
      <div class="box-body">
        <p><i class="fa fa-phone"></i><span style=""> Phone : 0800 000 000</span></p>
        <p><i class="fa fa-home"></i><span style=""> Web : http://www.example.com</span></p>
        <p><i class="fa fa-map-marker"></i><span style=""> Map : example map address</span></p>
        <p><i class="fa fa-envelope"></i><span style=""> Email : example@address.com</span></p>
      </div><!-- /.box-body -->
    </div><!-- /.box -->
</div>

This css code works correctly for the all the html on the page:

<style type="text/css">
    i{width: 30px;}
</style>

How can I specify the i class in the box1 box-body class?

Here is the code that I have tried:

<style type="text/css">
    box1 box-body i{width: 30px;}
</style>

Thanks in advance.

回答1:

In CSS, classes need to be prefixed by a ., ids need to be prefixed by #, and elements don't need to be prefixed at all.

This is how you need to declare your CSS:

.box1 .box-body i {
   width: 30px;
}

Note that box1 and box-body are both classes, while i is an element.

Example:

<div class="class"></div>
<div id="id"></div>
<div></div>

I have listed three different <div> elements. This is how they would be accessed in CSS:

// first div
.class {
[some styling]
}

// second div
#id {
[some styling]
}

// third div
div {
[some styling]
}

回答2:

The classes in your CSS need periods before them. Note i doesn't since it's an element not a class.

<style type="text/css">
    .box1 .box-body i{width: 30px;}
</style>

回答3:

Selectors for classes in CSS need a ".":

.box1 .box-body i{/*your style*/}

Maybe you should take a look at this page:

Selectors

回答4:

   <style type="text/css">
   .box1 .box-body i{width: 30px;}
   </style>

回答5:

You just need to know how css selectors work. Here is brief description about css selectors.

In your case,

.box .box-body i{
  width:30px;
}

space between two selectors defines second element is child of first. In your case, element i is child element of element which has box-body class. and that element is child element of class which has .box class.

来源：https://stackoverflow.com/questions/30505225/how-to-reference-nested-classes-with-css

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