html, body {
    margin: 0;
    height: 100%;
    background: #000;
    color: #d8f5ff;
    font-family: "VT323", "Consolas", ui-monospace, monospace;
    overflow: hidden;
}

.app {
    position: relative;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 1rem;
    box-sizing: border-box;
    background:
        radial-gradient(circle at 20% 25%, rgba(216, 245, 255, 0.08), transparent 18rem),
        radial-gradient(circle at 80% 75%, rgba(216, 245, 255, 0.06), transparent 16rem),
        #000;
}

.menu-btn {
    position: fixed;
    top: 1.4rem;
    left: 0.6rem;
    z-index: 100;
    background: rgba(0, 0, 0, 0.55);
    color: #e6ecf0;
    border: 1px solid rgba(200, 220, 225, 0.5);
    border-radius: 6px;
    padding: 0.35rem 0.75rem;
    font: 600 0.85rem/1 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
    letter-spacing: 0.18em;
    text-decoration: none;
    -webkit-tap-highlight-color: transparent;
    pointer-events: auto;
}

.menu-btn:hover {
    background: rgba(216, 245, 255, 0.14);
}

.overlay {
    position: absolute;
    inset: 0;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 1.5rem;
    padding: 1rem;
    box-sizing: border-box;
    background: rgba(0, 0, 0, 0.72);
    text-align: center;
    z-index: 5;
}

.overlay.hidden {
    display: none;
}

.overlay__title {
    color: #fff;
    font-size: clamp(2rem, 8vw, 4.5rem);
    letter-spacing: 0.35em;
    line-height: 1;
    text-indent: 0.35em;
    text-shadow: 0 0 12px rgba(216, 245, 255, 0.7);
}

.app.is-start .board-wrap {
    display: none;
}

.btn {
    background: transparent;
    color: #d8f5ff;
    border: 2px solid #d8f5ff;
    border-radius: 0;
    padding: 0.5rem 1.1rem;
    font-family: inherit;
    font-size: 1.3rem;
    letter-spacing: 0.2em;
    text-transform: uppercase;
    cursor: pointer;
    text-shadow: 0 0 6px rgba(216, 245, 255, 0.55);
    box-shadow: 0 0 10px rgba(216, 245, 255, 0.22);
    -webkit-tap-highlight-color: transparent;
    touch-action: manipulation;
}

.btn:hover {
    background: rgba(216, 245, 255, 0.15);
}

.btn--vector {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.65rem;
}

.btn--vector svg {
    width: 1.35rem;
    height: 1.35rem;
}

.icon-restart,
.app.is-over .icon-start {
    display: none;
}

.app.is-over .icon-restart {
    display: block;
}

.board-wrap {
    width: min(78vmin, 780px);
    aspect-ratio: 7 / 6;
    filter: drop-shadow(0 0 14px rgba(216, 245, 255, 0.28));
}

#board {
    display: block;
    width: 100%;
    height: 100%;
    background: #000;
}