Tests that media query stack is computed correctly when several stylesheets share the same URL.

Main style:
[expanded] 
element.style { ()

[expanded] 
#main { (<style>)
    color: white;

[expanded] 
#main { (<style>)
    background: blue;

[expanded] 
div { (user agent stylesheet)
    display: block;
    unicode-bidi: isolate;