body {
    min-height: 100%;
    position: relative;
}
#main {
    margin: 10px auto;
    text-align: center;
}
#buttons {
    margin: 10px;
}
button {
    margin: 8px 0;
}
#progress {
    margin: 15px;
}
.box {
    display: inline-block;
    width: 50px;
    height: 50px;
    margin: 0 2px;
    box-sizing: border-box;
    border: 1px solid black;
    overflow: hidden;
    color: red;
    position: relative;
}
.box .dirt {
    z-index: 0;
    font-size: 18px;
    /* position: absolute;
    top: 0px;
    left: 6px; */
}

.box #vacuum-cleaner {
    position: absolute;
    top: 10px;
    right: 12px;
    z-index: 1;
    width: 20px;
    height: 20px;
    background-color: black;
    border-radius: 50%;
    padding: 3px;
    color: white;
}

footer {
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
}