First and last column has padding

The following rules are defined in the columns.css (xwiki-platform/blob/master/xwiki-platform-core/xwiki-platform-web/xwiki-platform-web-war/src/main/webapp/resources/uicomponents/container/columns.css):

.container-columns .first-column {
  padding-left: 0;
}
.container-columns .last-column {
  padding-right: 0;
} 

So the first line shouldn't have any padding on the left, and the last line shouldn't have any on the right.

This bug appears to have been present since May 4, 2015, with the commit [XWIKI-10118] Generate column-specific css definitions instead of providing only one layout, and therefore does not appear to be critical. Here, the padding was added to a block that comes after the rules, making it a higher-priority rule, so the rules no longer have any effect.

The problem is solved when the padding is defined again in the .container-columns .column rule (line 19), rather than having to define it every time.