<html>
<head>
    <style>
        div {
            float: left;
        }

        #box1 {
            height: 50px;
            width: 25px;
            background-color: orange;
        }
        #box2 {
            height: 25px;
            width: 25px;
            background-color: blue;
        }
        #box3 {
            height: 25px;
            width: 25px;
            clear: left;
            background-color: magenta;
        }
    </style>
</head>
<body>
    <div id="box1"></div>
    <div id="container">
        <div id="box2"></div>
        <div id="box3"></div>
    </div>
</body>
</html>