metamask-extension/ui/css/itcss/settings/variables.scss

// Flex
%row-nowrap {
  display: flex;
  flex-flow: row nowrap;
}

%col-nowrap {
  display: flex;
  flex-flow: column nowrap;
}

// Background Image Sizing
%bg-contain {
  background-size: contain;
  background-repeat: no-repeat;
  background-position: center;
}

%ellipsify {
  text-overflow: ellipsis;
  white-space: nowrap;
  overflow: hidden;
}