body {
    background-color: cyan;
}

#arena {
    width: 50%;
    max-width: 400px;
    margin: 60px auto 0;
    display: flex;
    flex-direction: column;
}

#arena-top {
    width: 100%;
    display: flex;
    flex-direction: row;
}

#left-border {
    display: flex;
    flex-direction: column;
    border-left: 1px solid white;
}

#content {
    display: flex;
    flex-direction: column;
}

.row-content {
    display: flex;
    flex-direction: row;
}

#right-border {
    display: flex;
    flex-direction: column;
    border-right: 1px solid white;
}

#bottom-border {
    display: flex;
    flex-direction: row;
    border-left: 1px solid white;
}

#bottom-border .box {
    border-bottom: 1px solid white;
}

#bottom-border .box:last-child {
    padding-right: 1px;
    border-right: 1px solid white;
}

.box {
    width: 24px;
    height: 24px;
    border: 1px solid gray;
    background-color: green;
}

.box-border {
    background-color: saddlebrown;
}

.box-empty {
    background-color: black;
}

.moving-box {
    background-color: white;
}

#game-over-span {
    color: red;
}

.d-none {
    display: none;
}

.d-initial {
    display: initial;
}