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<div class="redbox" id="redbox-01"></div>

body {
    background-color: rgba(0, 0, 0, 0.2);
}
.redbox {
    position: absolute;
    min-width: 50px;
    height: 50px;
    background-color: #f00;
    top: 25px;
    left: 25px;
    color: #fff;
    text-align: center;
    padding: 1.0em 0.8em 0 0.8em;
    font-family: monospace;
    font-size: 1.4em;
}