Only a CSS change is required. I use:
.tocheader a {text-decoration:none; padding:0 3px 1px; background-color:#fcfcfc; border:1px solid rgb(140, 172, 187);}
or take a look here
http://wiki.jalakai.co.uk/dokuwiki/doku.php?id=tutorials:navigation_sidebar
Personally, I think the -/+ could be moved in front of the "Table of Contents" text, but its no big deal :)