<div id="encabezado">
<img id="logo2" src="imagenes/ppal/grupo.png"/>
<div></div>
<center><img id="logo" src="imagenes/ppal/bibliosis.png"/></center>
</div>
@media screen and(max-width:400px){
#logo2{display: none}
}
@media screen and(max-width:400px){
@media screen and (max-width:400px){
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<style>
@media screen and (max-width:400px){
#logo2{display: none;}
}
</style>
</head>
<body>
<div id="encabezado">
<img id="logo2" src="imagenes/ppal/grupo.png"/>
<div></div>
<center><img id="logo" src="imagenes/ppal/bibliosis.png"/></center>
</div>
</body>
</html>