What's the trick to modify the disclosure icon in a list x-type? I found a few posts that describe the CSS overrides to use, but they do not work for me for some reason. The selector appears to be recognized, but the result is a solid blue box where the disclosure icon would normally be located. Here's the CSS I'm using (and the only way that I can even get the icon to change at all):
#foo.x-list .x-list-disclosure {-webkit-mask-image: url('images/disclosure1.png') !important;
width: 24px;
height: 24px;
-webkit-mask-size: 24px 24px;
}