Sticky table header problem

This great theme has a problem with the new sticky table headers in 6.x, a great improvement very notable at the permissions page in admin. In Atlantis theme it just show as a white box though, no text. Reason for this is background is set to #fff in core system.css

Maybe there is a smoother solution to this then my clumpsy workaround, which either is to edit /modules/system/system.css (which is a bad solution) or somewhat better but still cumpsy, copy system.css into theme folder, edit

/*
** Floating header for tableheader.js
*/
table.sticky-header {
  margin-top: 0;
  background: #fff;
}

to become

/*
** Floating header for tableheader.js
*/
table.sticky-header {
  margin-top: 0;
  background: #1F7CAF;
}

and in a3_atlantis.info add

+stylesheets[all][] = system.css
stylesheets[all][] = style.css

the latter works fine, but as the only thing that need to change is 'background: #1F7CAF;', it feels a bit overkill. But if nothing else, at least it solves the problem. It might be worth though to raise the question if this class shouldn't move to style.css as it ought to cause problem for all themes using light/white text on darker background.