icon-Startup Search
You can try the following: the icon class should be the first in the attribute:
[class^='icon-'].btn
In this HTML
<div class="icon-1 btn">Foo</div>
<div class="icon-2 btn">Bar</div>
<div class="btn icon-3">Fizz</div>
<div class="icon btn">Buzz</div>
Search icon-Inside (Warning!)
You can modify the query to base a class search in a substring:
[class*='icon-'].btn
, , icon-, myicon-1 noicon-2.
icon-
, icon- , :
[class^='icon-'].btn, [class*=' icon-'].btn
icon- ( ).
<div class="icon-1 btn">Foo</div>
<div class="icon-2 btn">Bar</div>
<div class="btn icon-3">Fizz</div>
<div class="icon btn">Buzz</div>