* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    padding: 16px;
    background: #fafafa;
    color: #222;
}

.header {
    margin-bottom: 16px;
}

.header h1 {
    font-size: 24px;
    font-weight: 600;
    margin-bottom: 6px;
}

.header a {
    color: #555;
    font-size: 14px;
}

/* --- 27x27 CSS Grid --- */

:root {
    --cell-size: clamp(18px, calc((95vw - 14 * 12px) / 13), 36px);
    --border-size: 12px;
}

.grid-container {
    display: flex;
    justify-content: center;
    margin-bottom: 20px;
}

.grid {
    display: grid;
    grid-template-columns: repeat(13, var(--border-size) var(--cell-size)) var(--border-size);
    grid-template-rows: repeat(13, var(--border-size) var(--cell-size)) var(--border-size);
    /* 13 pairs + 1 trailing = 27 tracks each axis */
    user-select: none;
    -webkit-user-select: none;
}

/* Cells */
.grid-cell {
    background: #fff;
    position: relative;
}

.grid-cell .clue-number {
    position: absolute;
    top: 1px;
    left: 2px;
    font-size: clamp(8px, calc(var(--cell-size) * 0.3), 12px);
    line-height: 1;
    color: #999;
    pointer-events: none;
}

/* Corners — always dark */
.grid-corner {
    background: #222;
}

/* Borders — shared base */
.grid-border {
    position: relative;
    cursor: pointer;
    background: transparent;
}

/* Outer-edge borders: always dark, not interactive */
.grid-border.outer {
    cursor: default;
}

/* The visual line inside a border element */
.grid-border::after {
    content: "";
    position: absolute;
    background: #ccc;
    transition: background 0.1s;
}

.grid-border.horiz::after {
    left: 0;
    right: 0;
    top: 50%;
    height: 1px;
    transform: translateY(-50%);
}

.grid-border.vert::after {
    top: 0;
    bottom: 0;
    left: 50%;
    width: 1px;
    transform: translateX(-50%);
}

/* Thick (active) border */
.grid-border.thick::after {
    background: #222;
}

.grid-border.horiz.thick::after {
    height: 3px;
}

.grid-border.vert.thick::after {
    width: 3px;
}

/* Outer borders are always thick and dark */
.grid-border.outer::after {
    background: #222;
}

.grid-border.horiz.outer::after {
    height: 3px;
}

.grid-border.vert.outer::after {
    width: 3px;
}

/* Hover effect for inner borders */
.grid-border:not(.outer):hover::after {
    background: #888;
}

.grid-border.horiz:not(.outer):hover::after {
    height: 3px;
}

.grid-border.vert:not(.outer):hover::after {
    width: 3px;
}

/* --- Buttons --- */

.actions {
    display: flex;
    gap: 10px;
    justify-content: center;
    margin-bottom: 20px;
    flex-wrap: wrap;
}

.actions button {
    font-size: 16px;
    padding: 10px 24px;
    min-height: 48px;
    border: 1px solid #ccc;
    border-radius: 6px;
    background: #fff;
    cursor: pointer;
    font-family: inherit;
}

.actions button:hover {
    background: #f0f0f0;
}

.actions button.primary {
    background: #222;
    color: #fff;
    border-color: #222;
}

.actions button.primary:hover {
    background: #444;
}

/* --- Output --- */

.output-section {
    max-width: 640px;
    margin: 0 auto;
}

.output-section pre {
    background: #fff;
    border: 1px solid #ddd;
    border-radius: 6px;
    padding: 16px;
    font-size: 13px;
    white-space: pre-wrap;
    word-break: break-word;
    font-family: "SF Mono", "Consolas", "Liberation Mono", monospace;
    margin-bottom: 10px;
    max-height: 60vh;
    overflow-y: auto;
}

.output-section .copy-btn {
    font-size: 14px;
    padding: 8px 16px;
    border: 1px solid #ccc;
    border-radius: 6px;
    background: #fff;
    cursor: pointer;
    font-family: inherit;
}

.output-section .copy-btn:hover {
    background: #f0f0f0;
}

/* --- Mobile --- */

@media (max-width: 600px) {
    body {
        padding: 10px;
    }

    .actions {
        flex-direction: column;
    }

    .actions button {
        width: 100%;
    }
}