style.css

html, body {
    padding: 0px;
    margin: 0px;
    height: 100%;
    background: url(background.svg);
    font-family: "HelveticaNeue-Light", "Helvetica Neue Light", "Helvetica Neue", Helvetica, Arial, "Lucida Grande", sans-serif;
    font-weight: 300;
    color: #555;
}
/* Page */
.page-area {
    display: grid;
    grid-template-columns: 1fr minmax(0px, 700px) 1fr;
    height: 100%;
}
.content-area {
    grid-column: 2 / 3;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: space-around;
}

/* Board */
.go-board-area {
    width: 100%;
}
svg {
    width: 100%;
    height: auto;
}
.hGrid-line, .vGrid-line {
    stroke: #555;
    stroke-width: 2px;
    stroke-linecap: round;
}
.grid-point {
    fill: #555;
}

/* Control */
.control-area {
    width: 90%;
    height: 100px;
    display: flex;
    justify-content: space-around;
    align-items: center;
}
.btn {
    height: 60px;
    width: 60px;
    border: 2px solid #555;
    display: flex;
    justify-content: center;
    align-items: center;

}
.btn:hover {
    background: white;
    cursor: pointer;
}
i {
    font-size: 2.7em;
    color: inherit;
    color: #555;
}
@media only screen and (max-width: 500px) {
    .btn {
        height: 40px;
        width: 40px;
    }
    i {
        font-size: 2em;
    }
}

/* Stones */
.stone {

}
.black {
    fill: #555;
}
.white {
    fill: white;
    stroke-width: 4px;
}
.preview {
    fill-opacity: 0.5;
}
.remove {
    fill: red;
    fill-opacity: 0.3;
}

/* Multiplayer */
.multiplayer-title {
    font-weight: bold;
    font-size: 1.7em;
}
.multiplayer-area {
    width: 90%;
    margin-top: 50px;
    margin-bottom: 100px;
    font-size: 1.5em;
}
.m-btn {
    display: inline-block;
    padding: 10px 15px;
    margin: 10px 0px;
    cursor: pointer;
    border: 2px solid #555;
}
.m-btn:hover{
    background: white;
}
.friend-area {
    display: none;
}
#friend-peer-id {
    font-size: 0.5em;
}
.status-msg {
    padding: 3px 10px 3px 10px;
    border: 2px solid #555;
}
#peer-id {
    font-weight: bold;
}