/* Theme variables (light by default) */
:root {
    --bg-gradient: linear-gradient(180deg, #f8fafc, #eef2f7);
    --page-bg: transparent;
    --surface-bg: #ffffff;
    --muted-text: #64748b;
    --text: #0f172a;
    --card-shadow: 0 6px 18px rgba(15, 23, 42, 0.08);
    --border: #e6e9ee;
    --accent: #0ea5e9;
    --accent-contrast: #ffffff;
    --cell-border: #d1d5db;
    --cell-bg: #ffffff;
    --marked-bg: #ef4444;
    --marked-text: #ffffff;
}

/* If user prefers dark, flip the variables */
@media (prefers-color-scheme: dark) {
    :root {
        --bg-gradient: linear-gradient(180deg, #071027, #07172a);
        --surface-bg: #071327;
        --muted-text: #9aa9bf;
        --text: #e6eef8;
        --card-shadow: 0 6px 18px rgba(2, 6, 23, 0.6);
        --border: #0f172a;
        --accent: #38bdf8;
        --accent-contrast: #07283a;
        --cell-border: #0b1420;
        --cell-bg: #052033;
        --marked-bg: #991B1B;
        --marked-text: #fff;
    }
}

/* Reset small defaults */
* {
    box-sizing: border-box;
}

html,
body {
    height: 100%;
    margin: 0;
    font-family: Inter, system-ui, -apple-system, 'Segoe UI', Roboto, 'Helvetica Neue', Arial
}

body {
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--bg-gradient);
    padding: 1rem;
    color: var(--text)
}

.container {
    width: 100%;
    max-width: 900px;
    margin: 0 auto
}

header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 1rem
}

    header h1 {
        text-align: left;
        margin: 0 0 1rem 0;
        font-size: 1.5rem;
        color: var(--text)
    }

/* Theme toggle button */
#themeToggle {
    background: transparent;
    border: 1px solid var(--border);
    padding: 0.35rem 0.6rem;
    border-radius: 8px;
    cursor: pointer;
    color: var(--text);
    display: inline-flex;
    align-items: center;
    gap: 0.4rem
}

    #themeToggle:focus {
        outline: 2px solid var(--accent);
        outline-offset: 2px
    }

.card {
    background: var(--surface-bg);
    border-radius: 12px;
    padding: 1rem;
    box-shadow: var(--card-shadow);
    margin-bottom: 1rem;
    border: 1px solid rgba(0, 0, 0, 0.03)
}

#controls textarea {
    width: 100%;
    min-height: 90px;
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 0.6rem;
    font-family: monospace;
    font-size: 0.95rem;
    color: var(--text);
    background: transparent
}

#controls input[type=file] {
    margin-top: 0.6rem
}

.actions {
    display: flex;
    justify-content: flex-end;
    gap: 0.5rem;
    margin-top: 0.6rem
}

button#generate,
button#generate3 {
    background: var(--accent);
    border: none;
    color: var(--accent-contrast);
    padding: 0.6rem 1rem;
    border-radius: 8px;
    font-weight: 600;
    cursor: pointer
}

    button#generate:active,
    button#generate3:active {
        transform: translateY(1px)
    }

button#generate3 {
    background: transparent;
    color: var(--text);
    border: 1px solid var(--border)
}

.board-wrap {
    display: flex;
    justify-content: center
}

#bingo {
    border-collapse: collapse;
    margin-top: 1em;
    width: 100%;
    max-width: 720px
}

    #bingo td {
        width: calc(100% / 5);
        height: 0;
        padding-top: calc(100% / 5);
        position: relative;
        border: 1px solid var(--cell-border);
        background: var(--cell-bg)
    }

    #bingo[data-size="3"] td {
        width: calc(100% / 3);
        padding-top: calc(100% / 3)
    }

        #bingo td > div {
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            padding: 0.5rem;
            text-align: center;
            user-select: none;
            font-size: 0.95rem;
            color: var(--text)
        }

.marked {
    background: var(--marked-bg) !important;
    color: var(--marked-text) !important
}

.visually-hidden {
    position: absolute !important;
    height: 1px;
    width: 1px;
    overflow: hidden;
    clip: rect(1px, 1px, 1px, 1px);
    white-space: nowrap
}

/* Responsive tweaks */
@media (max-width:480px) {
    header h1 {
        font-size: 1.25rem
    }

    button#generate,
    button#generate3 {
        flex: 1
    }

    .actions {
        justify-content: stretch
    }
}