How to stop this text from going off the screen

There is a bug in the author's theme.

The author released a fix a couple of days ago.

The updated theme is on the author's site GitHub you will need to copy the updated theme code into the Edit HTML area.

EDIT: The theme has been moved to GitHub however, as of 2012 it is no longer being maintained.

I know how! Look for {block:HasTags} in your theme HTML. Around the <a href="{TagURL}">{Tag}</a> you can add HTML tags that change the layout such as font colour, font size, font style, etc. See below for an example:

{block:HasTags}
       {block:Tags}
          <font size="2"> 
          <font color="#FFFFFF">
          <a href="{TagURL}">{Tag}</a>
          </font>
          </font>
       {/block:Tags}
    {/block:HasTags}

I hope that helps!

Now I'm just trying to figure out how to automatically place a comma after each tag, but not when there is just one tag displayed. ;__;