.c4-board {
    display: grid; grid-template-columns: repeat(7, 1fr); gap: 6px;
    background: #4263eb; padding: 10px; border-radius: 16px;
    max-width: 420px; margin: 0 auto 1rem;
}
.c4-cell {
    aspect-ratio: 1; background: #fff; border-radius: 50%;
    display: flex; align-items: center; justify-content: center;
    font-size: clamp(1.2rem, 6vw, 2rem); cursor: pointer;
    box-shadow: inset 0 2px 4px rgba(0, 0, 0, .2);
}
.c4-cell:hover { background: #eef2ff; }
.c4-win { box-shadow: 0 0 0 3px #69db7c, inset 0 2px 4px rgba(0, 0, 0, .2); }