/* https://jsbin.com/bofitujaho/2/edit?html,css,output */ 

* {
  box-sizing: border-box;
}

div {
	
	
	display: flex;
	flex-wrap: wrap;
	width: 100%;
	border: 0px solid black;
	gap: 20px;
	border: 3px solid black;
	
}

span 
{
	background: red;
	 
	width: calc(25% - 15px);
	/*
		((pocet sloupcu - 1 ) * gap)  / poctem sloupcu
	*/
}