<p id="seg">Seg</p>
<p id="ter">Ter</p>
<p>test - only works on refresh so see other demo (https://codepen.io/paulobrien/pen/BjzWKw)</p>

html, body {
	margin:0;
	padding:0
}

@media screen and (max-width:399px){
	
	body{background:red}
	
}

if (window.matchMedia("(max-width: 399px)").matches) {
document.getElementById("seg").remove();
document.getElementById("ter").remove();
}