Sorry for the late reply, but can you be more precise about your request Aramis?

Are you talking about thumbnails inside a category like on http://piwigo.org/demo/index.php?/category/America or the list of categories like on http://piwigo.org/demo/index.php?/category/14 ?

(a screenshot with red arrows to tell where you need space would be very useful) and tell us which theme your currently using, it would help :-)

OK I see, it's much more precise now :-) (and easier to answer, of course).

First, I see that you have customized the "Sylvia" theme. Please, take the time to create another theme and overload some parameters. For example, you should create the theme "Aramis" (obviously, you like French swords ;-)

In the Aramis/themeconf.inc.php you should have something like:

<?php
/*
Theme Name: Aramis
Version: 1
Description: Dark background, blue decorations; derived from Sylvia
Theme URI: http://piwigo.org/ext/extension_view.php?eid=???
Author: Marek Jeziorski
Author URI: http://oneblade.pl
*/
$themeconf = array(
  'name'         => 'Aramis',
  'parent'        => 'Sylvia',
  'icon_dir'      => 'themes/Aramis/icon',
);
?>

Then copy the themes/Sylvia/icon directory as themes/Aramis/icon and restore the original Sylvia icons.

Then create a themes/Aramis/themes.css file:

.content ul.thumbnails span.wrap1 {margin-left:15px;}

It is important that you don't modify the standard files (such as Sylvia themes) to avoid any loss during next upgrade (upgrades assure you're running with the latest and most secure version of Piwigo)