you can put a border round anything it looks good on hover over links. To put a border in just paste this before the } in the bit you want,
border:NUMBERpx STYLE COLOUR;
change number to a low number i suggest 1 or 2.
change style to either solid for a normal line, dashed or dotted,(dotted is what I have on my links when you hover over).
change colour to a colour.
If you want each side of the border to be different use this,
border-top:NUMBERpx STYLE COLOUR;
border-bottom:NUMBERpx STYLE COLOUR;
border-left:NUMBERpx STYLE COLOUR;
border-right:NUMBERpx STYLE COLOUR;
change the things in caps like before^