Changing width of allowable tabs(?)

Two options – you may need to combine them:
1. Change the size of the text
2. Change the padding on the left and right – it’s currently 20px, you could get away with 10 quite comfortably.

You’ll need to edit/add CSS – if it’s only small overrides like this, you can use the Jetpack plugin (jetpack.me/support/custom-css) to add them in the dashboard.

In terms of the specific CSS you need, try this:

#nav li {
margin: 0;
}

#nav li a:link, #nav li a:visited {
font-size: 12px;
padding-left: 10px;
padding-right: 10px;
}