style.css

#gameContainer {
    position: absolute;
    width: 520px;
    height: 520px;
    background-color: #000000;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

#elementsContainer {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}
/**
left bar
 */
#sidebar {
    position: absolute;
    top: 0;
    right: 520px;
    width: 180px;
    height: 480px;
    background-color: #ccc;
    padding: 20px;
    text-align: center;
}

/**
right bar for second player
 */
#sidebarSecond {
    position: absolute;
    top: 0;
    right: -220px;
    width: 180px;
    height: 480px;
    background-color: #ccc;
    padding: 20px;
    text-align: center;
}



.heart {
    width: 50px;
    height: 50px;
    background-image: url(images/heart.png);
    background-size: 50px 50px;
    position: absolute;
}

.heatHeart {
    width: 50px;
    height: 50px;
    background-image: url(images/heatHeart.png);
    background-size: 50px 50px;
    position: absolute;
}

#tank {
    width: 40px;
    height: 40px;
    background-image: url(images/tankImage.png);
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    position: absolute;
    top: 480px;
    left: 160px;
}

#tankSecond {
    width: 40px;
    height: 40px;
    background-image: url(images/tankImage2.png);
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    position: absolute;
    top: 0px;
    left: 320px;
    transform: rotate(180deg);
}

.bulletTop {
    width: 5px;
    height: 10px;
    background-color: #0f0;
    position: absolute;
}

.bulletLeft {
    width: 10px;
    height: 5px;
    background-color: #0f0;
    position: absolute;
}

.obstacle2 {
    width: 39px;
    height: 39px;
    background-image: url(images/block2.png);
    background-size: 40px 40px;
    position: absolute;
}

.water.obstacle2 {
    width: 40px;
    height: 40px;
    background-image: url(images/blockWater.jpg);
    background-size: 40px 40px;
    position: absolute;
}

.breakable.obstacle2 {
    width: 39px;
    height: 39px;
    background-image: url(images/block.png);
    background-size: 40px 40px;
    position: absolute;
}

#gameCanvas {
    border: 1px solid #ffffff;
}