#game-board {
    width: 500px;
    margin: 20px auto 0 auto;
    background-color: #E288A0;
    background-color: rgba(255,255,255,0.5);

    border: 7px solid #B71F45;
    padding: 20px;
    border-radius: 10px;
    overflow: hidden;
}
.circle {
    border-radius: 50%;
    width: 75px;
    height: 75px;
    border: 1px solid #000;
    float: left;
}
.clear-float {
    clear: both
}

#game-board {
    width: 400px;
    margin: 20px auto 0 auto;
    background-color: #E288A0;
    background-color: rgba(255,255,255,0.5);

    border: 7px solid #B71F45;
    padding: 20px;
    border-radius: 10px;
    overflow: hidden;
}
.circle {
    border-radius: 50%;
    width: 75px;
    height: 75px;
    border: 1px solid #000;
    float: left;
}
.clear-float {
    clear: both
}

Adjust size of border around spheres
Adjust size of border around spheres
