Sass 4

$totalWidth: 940px;
$columnCount: 5;
@function getColumnWidth($width, $count){
	$padding: 10px;
	$columnWidth: floor($width - ($padding * ($count - 1) / $count));
	@debug $columnWidth;
	@return $columnWidth;
}

.grid {
	float: left;
	width: getColumnWidth($totalWidth, $columnCount);
}

@mixin round {
	border-radius: 4px;
}

.label {
	font-size: 12px;
	@include round;
}

.msg {
	font-size: 12px;
	font-weight: bold;
	padding: 2px 4px;
	color: white;
}

.errorMsg {
	@extend .msg;
	background: red;
}

.warningMsg {
	@extend .msg;
	background: orange;
}

.msg, .errorMsg, .warningMsg {
  font-size: 12px;
  font-weight: bold;
  padding: 2px 4px;
  color: white;
}

.errorMsg {
  background: red;
}

.warningMsg {
  background: orange;
}

OK! 比較的いいペース