#board { border: 1px solid black; display: inline-block; }
#board > div {display: table; border: 2px solid yellow;}
#board > div > div {display: table-row;}
#board > div > div > div {display: table-cell; border: 2px solid yellow;} 
#board > div > div > div > div {display: table;}
#board > div > div > div > div > div {display: table-row;}
#board > div > div > div > div > div > div { display: table-cell; width: 40px; height: 40px;
    vertical-align:middle; text-align: center; border: 1px solid black;}