This has been tested in Vector in a large number of browsers to not have side effects and only making the underline no longer shine through transparent borders or margins of thumbs.
Also, due to float clearing abilities of overflow:hidden (it's all over the internet) this also causes the editsection link to no longer be stacked down (see en.wiki WP:BUNCH), see bug 26449.
background: none;
font-weight: normal;
margin: 0;
+ overflow: hidden;
padding-top: .5em;
padding-bottom: .17em;
border-bottom: 1px solid #aaa;