Allow sub-themes to override wireframes.css

When I enable wireframes and add to layout.css of my sub-theme in #content-inner margin-top: 150px this value becomes overwritten by wireframes.css in a default setup (meaning build a sub-theme by following README.txt to copy STARTERKIT). wireframes.css is referenced second last in html-header before print.css.

I get the meaning of wireframes wrong but I'd only expact it to frame divs and other (html-)blocks but do nothing to positioning of divs.

Opera Dragonfly sais this:

wireframes.css
#header-inner, #content-inner, #content-inner > *, #navbar-inner, #sidebar-left-inner, #sidebar-right-inner, #footer-inner {
  margin-top: 1px;
  margin-right: 1px;
  margin-bottom: 1px;
  margin-left: 1px;
  padding-top: 2px;
  padding-right: 2px;
  padding-bottom: 2px;
  padding-left: 2px;
  border-top-color: #cccccc;
  border-left-color: #cccccc;
  border-right-color: #cccccc;
  border-bottom-color: #cccccc;
  border-top-width: 1px;
  border-left-width: 1px;
  border-right-width: 1px;
  border-bottom-width: 1px;
  border-top-style: solid;
  border-left-style: solid;
  border-right-style: solid;
  border-bottom-style: solid
}
layout.css
#content-inner {
  margin-right: 0 [overwritten];
  margin-bottom: 0 [overwritten];
  margin-left: 0 [overwritten];
  padding-top: 0 [overwritten];
  padding-right: 0 [overwritten];
  padding-bottom: 0 [overwritten];
  padding-left: 0 [overwritten];
  margin-top: 150px [overwritten];
  height: 300px;
  max-height: 300px
}