Make ui_tables look like they belong

I humbly submit a few lines of css to make `ui_table` sections of webmin look a little more like they fit in (e.g. the "Others/Upload and Download" page shows the difference before and after pretty well. It's not perfect, but it goes a long way to make the bits of Webmin I use a lot look as nice as the rest of your very pretty (and useable) theme.

I did two commits because I don't use Github very often, but I *think* it's coalesced them all into one here.

Grazie!