body {
    text-align: center;
    background-color: rgba(47, 79, 79, 0.726);
    margin: 0;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    font-family: Arial, Helvetica, sans-serif;
}

h1 {
    margin-bottom: 0.25rem;
}

h2 {
    margin-top: 0.25rem;
    font-size: 1.2rem;
    cursor: pointer;
    user-select: none;
}

.btn-container {
    display: flex;
    flex-direction: column;
    align-items: center;
}

.line1, .line2 {
    display: flex;
}

.btn {
    height: 150px;
    width: 150px;
    border-radius: 20%;
    border: 10px solid black;
    margin: 1rem;
    cursor: pointer;
    user-select: none;
    font-size: 1.5rem;
    font-weight: bold;
    color: rgba(0, 0, 0, 0.3);
    display: flex;
    align-items: center;
    justify-content: center;
    transition: transform 0.1s;
}

.yellow {
    background-color: #f99b45;
}

.green {
    background-color: #819ff0;
}

.purple {
    background-color: rgba(121, 39, 121, 0.767);
}

.red {
    background-color: #d95980;
}

.btnflash {
    filter: brightness(2.5);
    box-shadow: 0 0 20px white;
    transform: scale(1.1);
}

.end {
    background-color: rgba(255, 0, 0, 0.5);
}

/* Responsive: tablets and small screens */
@media (max-width: 600px) {
    .btn {
        height: 110px;
        width: 110px;
        margin: 0.6rem;
        border-width: 7px;
        font-size: 1.2rem;
    }
    h1 {
        font-size: 1.5rem;
    }
    h2 {
        font-size: 1rem;
    }
}

/* Responsive: very small screens */
@media (max-width: 400px) {
    .btn {
        height: 80px;
        width: 80px;
        margin: 0.4rem;
        border-width: 5px;
        font-size: 1rem;
    }
    h1 {
        font-size: 1.2rem;
    }
    h2 {
        font-size: 0.9rem;
    }
}