Fix link spacing and underline on new homepage

In about:preferences for example, there is a standard gap between the string and link of around 10px. The underline style also looks more noticeable in about:preferences too – i.e. it seems to be offset slightly against the text, and is thicker.

Could we update the link style on the new homepage (i.e. new tab page; about:tor) to match please?

(Also, as mentioned previously – the new homepage should be using system fonts like other internal pages rather than Arial/Helvetica – however this may have been fixed since the last macOS Nightly already)