html, body {
    margin: 0;
    overflow: hidden;
    -webkit-user-select:none;
    -moz-user-select:none;
    -ms-user-select:none;
    user-select:none;
}

h2{
    margin: 0;
    padding: 0;
}

.control-button{
    position: fixed;
    padding: 0.5rem 1rem;
    font-size: 14px;
    cursor: pointer;
    border: 1px solid #ccc;
    border-radius: 8px;
    background: white;
    z-index: 999;
}

#toggleGravity{
    bottom: 1.5rem;
    right: 1.5rem;
}

#toggleBlackHole{
    bottom: 1.5rem;
    right: 10.5rem;
}

#toggleBlackHole.active {
    background: #111;
    border-color: #111;
    color: #fff;
}

.black-hole {
    position: fixed;
    left: 50%;
    top: 50%;
    width: 96px;
    height: 96px;
    transform: translate(-50%, -50%);
    border-radius: 50%;
    pointer-events: none;
    z-index: 998;
    will-change: transform, opacity;
    background:
        radial-gradient(circle at center, #020202 0 24%, rgba(16, 8, 45, 0.98) 38%, rgba(51, 14, 118, 0.92) 50%, rgba(0, 183, 255, 0.6) 63%, rgba(255, 255, 255, 0.12) 70%, transparent 76%),
        radial-gradient(circle at center, rgba(255, 255, 255, 0.22), transparent 60%);
    box-shadow:
        0 0 28px rgba(0, 157, 255, 0.45),
        0 0 70px rgba(127, 0, 255, 0.42),
        inset 0 0 16px rgba(255, 255, 255, 0.18);
    filter: saturate(1.2) contrast(1.08);
}

.black-hole::before,
.black-hole::after {
    content: '';
    position: absolute;
    inset: -16px;
    border-radius: 50%;
    animation: blackHoleSpin 2.4s linear infinite;
}

.black-hole::before {
    border: 2px solid rgba(255, 255, 255, 0.14);
    box-shadow:
        0 0 26px rgba(255, 255, 255, 0.12),
        inset 0 0 18px rgba(255, 255, 255, 0.08);
}

.black-hole::after {
    inset: -44px;
    border: 18px solid rgba(170, 225, 255, 0.08);
    box-shadow:
        0 0 28px rgba(145, 220, 255, 0.2),
        inset 0 0 20px rgba(255, 255, 255, 0.08);
    backdrop-filter: blur(1.5px) brightness(1.15) saturate(1.25);
    -webkit-backdrop-filter: blur(1.5px) brightness(1.15) saturate(1.25);
    animation-direction: reverse;
    animation-duration: 3.6s;
}

@keyframes blackHoleSpin {
    from {
        transform: rotate(0deg) scale(0.92);
    }
    to {
        transform: rotate(360deg) scale(1.08);
    }
}