I know this post is getting outdated, but here's what they asked.
In your style sheet:
.social {
width: 330px;
height: 75px;
float: right;
text-align: left;
padding: 10px 0;
border-bottom: dotted 1px #6d6d6d;
}
[class~="first"] {
padding-top:0;
}
[class~="last"] {
border:0;
}
But it may be a bad way to use selectors. Also, if you need multiple "first" extension, you'll have to be sure to set different name, or to refine your selector.
[class="social first"] {...}
I hope this will help someone, it can be pretty handy in some situation.
For exemple, if you have a tiny piece of css that has to be linked to many different components, and you don't want to write a hundred time the same code.
div.myClass1 {font-weight:bold;}
div.myClass2 {font-style:italic;}
...
div.myClassN {text-shadow:silver 1px 1px 1px;}
div.myClass1.red {color:red;}
div.myClass2.red {color:red;}
...
div.myClassN.red {color:red;}
Becomes:
div.myClass1 {font-weight:bold;}
div.myClass2 {font-style:italic;}
...
div.myClassN {text-shadow:silver 1px 1px 1px;}
[class~=red] {color:red;}