<div class='target'></div>
$unit: 1em;

.target {
	width: 18*$unit; height: 18*$unit;
	background: radial-gradient(
		#000 calc(#{$unit} - 1px), 
		transparent $unit, 
		transparent calc(#{3*$unit} - 1px), 
		#000 3*$unit, 
		#000 calc(#{5*$unit} - 1px), 
		transparent 5*$unit, 
		transparent calc(#{7*$unit} - 1px), 
		#000 7*$unit, 
		#000 calc(#{9*$unit} - 1px), 
		transparent 9*$unit
	);
}
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