<!DOCTYPE html><html><head><metacharset="utf-8"><metaname="viewport"content="width=device-width, initial-scale=1"><title></title><styletype="text/css">div {
background: red;
}
@media (max-width: 300px) {
div {
background: purple;
}
}
h2 {
color: white;
}
</style></head><body><div><h2>Mi primer diseño responsivo</h2></div></body></html>
