<!DOCTYPE html>

<html>
<head>
    <style>
        .box {
          width: 200px;
          height: 200px;
          margin: 10px;
          background-color: blue;
        }
        
        .composited {
          -webkit-transform: translateZ(0);
        }
        
        .clipped {
            -webkit-clip-path: inset(0 30px);
        }
        
        .masked {
            -webkit-mask: linear-gradient(transparent, black);
        }
        
    </style>
</head>
<body>

<div id="gain-mask" class="masked clipped composited box"></div>
<div id="lose-mask" class="clipped composited box"></div>

</body>
</html>