body {
    text-align: center;
    background-color: #1a237e;
    color: #FFFFFF;
}

h3 {
    margin: 1rem;
    color: #FFFFFF;
}

.btn {
    height: 200px;
    width: 200px;
    border-radius: 20%;
    border: 10px solid black;
    margin: 2rem;
}

.btn_container {
    display: flex;
    justify-content: center;
}

.yellow {
    background-color: yellow;
}

.red {
    background-color: red;
}

.blue {
    background-color: blue;
}

.green {
    background-color: green;
}

.flash {
    background-color: white;
}

.userFlash {
    background-color: gold;
}

#rules, #score {
    margin: 1rem auto;
    padding: 0.5rem;
    border: 1px solid #FFFFFF;
    max-width: 400px;
    text-align: left;
    color: #FFFFFF;
}

@keyframes glow {
    0%, 100% {
        box-shadow: 0 0 10px white, 0 0 20px white, 0 0 30px white;
    }
    50% {
        box-shadow: 0 0 20px red, 0 0 40px red, 0 0 60px red;
    }
}

.glow {
    animation: glow 0.5s alternate infinite;
}