style.css

body {
    padding: 0;
    margin: 0;
}

.wrapper {
    width: 100vw;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: flex-start;
}

.background-image {
    position: absolute;
    height: 100%;
    width: 100%;
    background-color: gray;
    opacity: 0.5;
    z-index: -1;
}

.game-settings {
    display: flex;
    flex-direction: column;
    align-items: center;
}

.game-settings--difficulty {
    margin: 16px;
}

.settings-button {
    height: 32px;
    border-radius: 5px;
    margin: 6px 0;
}

.settings-button:active {
    background-color: gray;
}

#playfield {
    border-spacing: unset;
    margin: 32px auto;
}

tr:first-child td {
    border-top: 20px solid #707070;
}

tr:last-child td {
    border-bottom: 20px solid #707070;
}

td {
    border: 10px solid #707070;
    width: 50px;
    height: 50px;
}

td:first-child {
    border-left: 20px solid #707070;
}

td:last-child {
    border-right: 20px solid #707070;
}

.red {
    background-color: #a13e43a1 !important;
}

.red-top {
    border-top-color: #93060e !important;
}
.red-right {
    border-right-color: #93060e !important;
}
.red-bottom {
    border-bottom-color: #93060e !important;
}
.red-left {
    border-left-color: #93060e !important;
}

.blue-top {
    border-top-color: #171565 !important;
}
.blue-right {
    border-right-color: #171565 !important;
}
.blue-bottom {
    border-bottom-color: #171565 !important;
}
.blue-left {
    border-left-color: #171565 !important;
}

.blue {
    background-color: #171565a3 !important;
}