Just a proposal:

/* Style bug rows according to severity. */
.bz_blocker { color: red; font-weight: bold; }
.bz_critical { color: red; }
.bz_major { color: #BB7000; }
.bz_normal { color: #000000; }
.bz_minor { color: #669900; }
.bz_trivial { color: #106581; }
.bz_enhancement { color: #777; background-color: white; }

/* Change background color in buglist for mouse over */
tr.bz_bugitem:hover {
    background-color: #f0f0f0;
}

/* Avoid underlining bug summaries, rather disruptive */
.bz_short_desc_column a, .bz_short_short_desc_column a {
    color: inherit;
    text-decoration: none;
}