<!doctype html>
<html>

<head>
    <meta charset="utf-8">
    <style>
        #gradient {
            width: 400px;
            height: 300px;
            background-image: linear-gradient(to right, black 0%, red 50%, gold 100%);
        }
    </style>
</head>

<body>
    <div id="gradient"></div>
</body>

</html>