body {
    font-family: sans-serif;
}

#board {
    width: 120px;  /* 10 cols × 12px */
    height: 240px; /* 20 rows × 12px */
    position: relative;
    background: #eee;
    border: 2px solid #000;
}

.cell {
    width: 12px;
    height: 12px;
    position: absolute;
    background: #00f;
    border: 1px solid #999;
    box-sizing: border-box;
}

#controls {
    margin-top: 10px;
}

.btn {
    display: inline-block;
    padding: 10px;
    margin: 4px;
    background: #555;
    color: white;
    font-size: 16px;
    width: 60px;
    text-align: center;
    border-radius: 4px;
}

.center {
    position: static;
    color: white;
    padding: 0px 92px;
    border: none;
    cursor: pointer;
}
 
.btn:active {
    background: #222;
}