Close button almost invisible

[Donato Marrazzo <donato marrazzo gmail com>]

Hello, I'm fedora 21 user.

In order to save vertical space, I tweaked the metacity-theme-3.xml

Specifically following lines:
<border name="title_border" left="10" right="10" top="0" bottom="0"/>

The result is good but as side effect the close button is almost invisible...

Is there a way to restore a human visible button?

Thank you