<!DOCTYPE html>
<head>
<style>
    button {
        position: relative;
        -webkit-appearance: none;
        border: 1px solid black;
        padding: 0;
    }

    .margin {
        margin: 5px 10px 5px 5px;
    }
    .sized {
        width: 50px;
        height: 50px;
    }
    .pink {
        background-color: pink;
    }
    .float {
        float: left;
    }
    .line {
        height: 2px;
        border-top: solid 1px #fff;
        background: #00f;

        position: absolute;
        width: 50px;
        bottom: 5px;
        left: 5px;
    }
</style>
</head>
<body>
    You should see an almost-square grey rectangle containing a pink square with a blue line below it.
    There should be no pink below the blue line.
<hr>
<button>
    <div class="margin sized float">
        <div class="sized">
            <div class="sized pink">
            <div class="line"></div>
        </div>
    </div>
</button>