:root {
    --primary: #2c3e50;
    --accent: #2980b9;
    --marked: #d35400;
    --bg: #f5f3ef;
    --card: #ffffff;
    --border: #d7dce0;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Arial, sans-serif;
}
body {
    font-family:
        -apple-system,
        BlinkMacSystemFont,
        "Segoe UI",
        Roboto,
        Helvetica,
        Arial,
        sans-serif;

    font-size: 17px;
    line-height: 1.75;

    background:
        radial-gradient(circle at top,
            #ffffff 0%,
            #f8f7f4 40%,
            #f2f0ec 100%);
    color: var(--primary);
    padding: 30px 20px 60px;
    display: flex;
    flex-direction: column;
    align-items: center;
}

/* HEADER */

header {
    text-align: center;
    margin-bottom: 24px;
}

header h1 {
    font-size: clamp(2rem, 5vw, 3rem);
    font-weight: 800;
    letter-spacing: -0.03em;
}

.subtitle {
    margin-top: 8px;
    color: #666;
}

/* LAYOUT */

.container {
    width: 100%;
    max-width: 850px;
    display: flex;
    flex-direction: column;
    gap: 25px;
    align-items: center;
}

/* INTRO */

.intro-card {
    width: 100%;
    max-width: 900px;
    background: white;
    padding: 28px;
    border-top: 4px solid var(--accent);
    border-radius: 12px;
    box-shadow: 0 10px 25px rgba(0,0,0,.06);
}

.intro-card h2 {
    margin-bottom: 12px;
    color: var(--primary);
}

.intro-card p {
    line-height: 1.7;
    color: #444;
}

.intro-card ul {
    margin: 15px 0 0 20px;
}

.paper-citation {
    margin-top: 15px;
    padding: 14px;
    background: #fafafa;
    border-left: 4px solid var(--accent);
    border-radius: 8px;
    font-family: Georgia, serif;
    color: #555;
    font-size: 0.9rem;
}
.quote {
    margin: 1rem 0;
    padding: 1rem 1.25rem;
    border-left: 4px solid #d1d5db;
    background: #f9fafb;
    color: #374151;
    font-style: italic;
    line-height: 1.7;
    border-radius: 0 4px 4px 0;
}


/* OPTIONAL COLLAPSIBLE INTRO */

.intro-wrapper {
    width: 100%;
    max-width: 900px;
}

.intro-wrapper summary {
    cursor: pointer;
    background: white;
    padding: 18px 22px;
    border-radius: 12px;
    font-weight: 700;
    box-shadow: 0 6px 20px rgba(0,0,0,.06);
}

/* BOARD */

.board {
    background: var(--card);
    padding: 24px;
    border-radius: 16px;
    box-shadow: 0 12px 30px rgba(0,0,0,.08);
    width: 100%;
    max-width: 850px;
    position: relative;
}

/* GRID */

.grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
}

/* CELLS */

.cell {
    position: relative;
    aspect-ratio: 1;

    display: flex;
    align-items: center;
    justify-content: center;

    padding: 10px;
    text-align: center;

    background: linear-gradient(#fafafa, #f1f3f5);
    border: 2px solid var(--border);
    border-radius: 10px;

    font-size: .9rem;
    font-weight: 600;

    cursor: pointer;
    user-select: none;
    transition: .2s;
}

.cell:hover {
    transform: translateY(-3px);
    border-color: var(--accent);
}

.cell.marked {
    background: #fff4e6;
    border-color: var(--marked);
    color: #7a3d00;
}

.cell.marked::before {
    content: "✕";
    position: absolute;
    font-size: 6rem;
    opacity: .15;
    z-index: 1;
}

.cell.free {
    background: #e8f4f8;
    border-color: var(--accent);
     font-size: 4rem;

}

/* TOOLTIP */

.tooltip {
    position: absolute;
    top: 105%;
    left: 50%;
    transform: translateX(-50%);

    width: 260px;

    background: #1f1f1f;
    color: white;

    padding: 12px;
    border-radius: 8px;
    font-size: .75rem;

    opacity: 0;
    visibility: hidden;
    transition: .15s ease;

    z-index: 9999;
}

.cell:hover .tooltip,
.tooltip:hover {
    opacity: 1;
    visibility: visible;
}

.tooltip a {
    display: block;
    margin-top: 10px;
    padding: 6px;

    background: #2b2b2b;
    border-radius: 6px;

    color: #7db7ff;
    text-decoration: none;
}

/* CONTROLS */

.controls {
    display: flex;
    gap: 15px;
    justify-content: center;
    margin-top: 20px;
}

button {
    border: none;
    cursor: pointer;

    padding: 10px 20px;
    border-radius: 8px;

    background: var(--primary);
    color: white;

    font-size: 1rem;
    font-weight: 600;

    transition: background .2s;
}

button:hover {
    background: var(--accent);
}

button.reset {
    background: #e74c3c;
}

button.reset:hover {
    background: #c0392b;
}

/* LEGEND */

.legend {
    width: 100%;
    max-width: 900px;

    background: white;
    padding: 24px;

    border-radius: 16px;
    box-shadow: 0 10px 25px rgba(0,0,0,.06);
}

.legend-header{background:#f8fafc;padding:14px;font-weight:700;cursor:pointer}
.legend-header p {
    color: #666;
}
.legend-content{display:none;padding:14px}


.legend-item{border:1px solid var(--border);border-radius:10px;margin-bottom:10px;overflow:hidden; padding:14px;   display: none;}
.legend-item.active {
    display: block;
    opacity: 1;
}

.citation {
    margin-top: 10px;
    padding-top: 10px;

    border-top: 1px solid #ddd;

    color: #666;
    font-size: .85rem;
    font-family: Georgia, serif;
}

/* MODAL */

.modal {
    display: none;
    position: fixed;
    inset: 0;

    background: rgba(0,0,0,.55);

    justify-content: center;
    align-items: center;

    z-index: 10000;
}

.modal-content {
    background: white;
    padding: 24px;
    border-radius: 12px;

    width: min(500px, 90vw);
}

.modal input,
.modal textarea {
    width: 100%;
    padding: 10px;
    margin-top: 10px;
}

.modal button {
    width: 100%;
    margin-top: 10px;
}

//* FOOTER */

.footer {
    margin-top: 30px;
    text-align: center;
    color: #777;
    font-size: .9rem;
}