I can confirm this bug with libgtksourceview2.0 on Ubuntu 12.04, gedit 3.4.1. Apart from the CSS property 'opacity', try also this:
div { color: white; /* correct highlighting */ border-radius: 4px; box-shadow: 5px 5px 10px 10px #abc; transform: rotate(90deg); }
I can confirm this bug with libgtksourceview2.0 on Ubuntu 12.04, gedit 3.4.1.
Apart from the CSS property 'opacity', try also this:
div {
color: white; /* correct highlighting */
border-radius: 4px;
box-shadow: 5px 5px 10px 10px #abc;
transform: rotate(90deg);
}