<style>
    .clearfix {
        clear: both;
    }
    .square {
        float: left;
        width: 49px;
        height: 49px;
    }
    .white {
        background-color: salmon;
        width: 100px;
        height: 100px;
    }
    .black {
        background-color: slateblue;
    }
</style>
<div>
    <div class="square white"></div>
    <div class="clearfix"></div>
    <div class="square black"></div>
</div>