#tubes {
    display: flex;
    margin: 20px;
    justify-content: center;
    margin-top: 50px;
    flex-wrap: wrap;
}
.tube {
    width: 50px;
    height: 180px;
    border: 2px solid var(--border-color, #E2E8F0);
    border-top: none;
    display: flex;
    flex-direction: column-reverse;
    margin: 0 10px;
    position: relative;
    border-radius: 0px 0px 30px 30px;
    padding: 1px;
}
.tube::after {
    content: attr(data-index);
    position: absolute;
    top: -20px;
    left: 50%;
    transform: translateX(-50%);
    font-size: 12px;
}
.ball {
    width: 44px;
    height: 44px;
    border-radius: 50%;
    box-sizing: border-box;
    border: 1px solid var(--border-color, #E2E8F0);
}

/* Dark mode: stronger tube borders for visibility */
body.dark-theme .tube {
    border-color: rgba(255, 255, 255, 0.35);
}
body.dark-theme .ball {
    border-color: rgba(255, 255, 255, 0.25);
}
button {
    margin: 10px;
    padding: 10px 20px;
    font-size: 16px;
}
@media (max-width: 480px) {
    #tubes {
        margin-top: 0px;
    }
    .tube {
        width: 40px;
        height: 160px;
        margin-top: 20px;
    }
    .ball {
    width: 40px;
    height: 40px;
    }
}