How to use aria-expanded="true" to change a css property

I want to use aria-expanded="true" to change a css property like an active class :

<li class="active">
   <a href="#3a" class="btn btn-default btn-lg" data-toggle="tab" aria-expanded="true"> 
       <span class="network-name">Google+</span>
   </a>
</li>

I want the <a> to background-color: #42DCA3 but only when aria-expanded="true".

Why javascript when you can use just css?

a[aria-expanded="true"]{
  background-color: #42DCA3;
}

<li class="active">
   <a href="#3a" class="btn btn-default btn-lg" data-toggle="tab" aria-expanded="true"> 
       <span class="network-name">Google+</span>
   </a>
</li>
<li class="active">
   <a href="#3a" class="btn btn-default btn-lg" data-toggle="tab" aria-expanded="false"> 
       <span class="network-name">Google+</span>
   </a>
</li>

li a[aria-expanded="true"] span{
    color: red;
}

<li class="active">
    <a href="#3a" class="btn btn-default btn-lg" data-toggle="tab" aria-expanded="true">
        <span class="network-name">Google+</span>
    </a>
</li>
<li class="active">
    <a href="#3a" class="btn btn-default btn-lg" data-toggle="tab" aria-expanded="false">
        <span class="network-name">Google+</span>
    </a>
</li>

li a[aria-expanded="true"]{
    background: yellow;
}

<li class="active">
    <a href="#3a" class="btn btn-default btn-lg" data-toggle="tab" aria-expanded="true">
        <span class="network-name">Google+</span>
    </a>
</li>
<li class="active">
    <a href="#3a" class="btn btn-default btn-lg" data-toggle="tab" aria-expanded="false">
        <span class="network-name">Google+</span>
    </a>
</li>

You could use querySelector() with attribute selector '[attribute="value"]', then affect css rule using .style, as you can see in the example below:

document.querySelector('a[aria-expanded="true"]').style.backgroundColor = "#42DCA3";

<ul><li class="active">
  <a href="#3a" class="btn btn-default btn-lg" data-toggle="tab" aria-expanded="true"> <span class="network-name">Google+ with aria expanded true</span></a>
  </li>
  <li>
    <a href="#3a" class="btn btn-default btn-lg" data-toggle="tab" aria-expanded="false"> <span class="network-name">Google+ with aria expanded false</span></a>
  </li>
</ul>

jQuery solution :

If you want to use a jQuery solution you could simply use css() method :

$('a[aria-expanded="true"]').css('background-color','#42DCA3');

Hope this helps.

If you were open to using JQuery, you could modify the background color for any link that has the property aria-expanded set to true by doing the following...

$("a[aria-expanded='true']").css("background-color", "#42DCA3");

Depending on how specific you want to be regarding which links this applies to, you may have to slightly modify your selector.