body:not + element:hover

HTML

<html>
  <body class="mobile">
    <h1>TITLE</h1>
    <div>
      <div class="btn">button</div>
    </div>
  </body>
</html>

CSS

.btn {
	background: blue;
	color: white;
	border-color: white;
}
body:not(.mobile) .btn:hover {
	background: red;
	color: blue;
	border-color: black;
}
.mobile .btn:active {
	background: red;
	color: blue;
	border-color: black;
}