:root {
    --background: #f7f7f5;
    --surface: #ffffff;
    --text-primary: #171717;
    --text-secondary: #6b6b6b;
    --border: #d8d8d4;
    --border-strong: #171717;
    --hidden-background: #eeeeeb;
    --button-hover: #eeeeeb;
    --radius-large: 28px;
    --radius-medium: 16px;
    --shadow: 0 16px 40px rgba(0, 0, 0, 0.07);
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    min-height: 100vh;
    background:
        linear-gradient(rgba(0, 0, 0, 0.025) 1px, transparent 1px),
        linear-gradient(90deg, rgba(0, 0, 0, 0.025) 1px, transparent 1px),
        var(--background);
    background-size: 28px 28px;
    color: var(--text-primary);
    font-family:
        "Noto Sans TC",
        "Noto Sans JP",
        system-ui,
        -apple-system,
        BlinkMacSystemFont,
        "Segoe UI",
        sans-serif;
}

button,
input {
    font: inherit;
}

button {
    color: inherit;
}

.kana-app {
    width: min(100% - 32px, 920px);
    margin: 0 auto;
    padding: 64px 0;
}

.page-header {
    margin-bottom: 40px;
    text-align: center;
}

.eyebrow {
    margin: 0 0 10px;
    color: var(--text-secondary);
    font-size: 0.78rem;
    font-weight: 700;
    letter-spacing: 0.16em;
    text-transform: uppercase;
}

h1 {
    margin: 0;
    font-size: clamp(2.2rem, 7vw, 4.4rem);
    line-height: 1.1;
    letter-spacing: -0.05em;
}

.description {
    max-width: 600px;
    margin: 18px auto 0;
    color: var(--text-secondary);
    line-height: 1.8;
}

.control-section {
    margin-bottom: 24px;
}

.control-section h2 {
    margin: 0 0 12px;
    font-size: 0.95rem;
}

.button-group {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 10px;
}

.mode-button,
.primary-button,
.secondary-button,
.text-button {
    border: 1px solid var(--border);
    cursor: pointer;
    transition:
        background-color 160ms ease,
        border-color 160ms ease,
        color 160ms ease,
        transform 160ms ease;
}

.mode-button {
    min-height: 48px;
    padding: 10px 14px;
    background: var(--surface);
    border-radius: 999px;
    font-weight: 700;
}

.mode-button:hover {
    background: var(--button-hover);
}

.mode-button.active {
    background: var(--text-primary);
    border-color: var(--text-primary);
    color: #ffffff;
}

.toggle-group {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 10px;
}

.toggle-option {
    display: flex;
    align-items: center;
    gap: 10px;
    min-height: 50px;
    padding: 12px 16px;
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--radius-medium);
    cursor: pointer;
}

.toggle-option:hover {
    border-color: #a6a6a0;
}

.toggle-option input {
    width: 18px;
    height: 18px;
    accent-color: var(--text-primary);
}

.toggle-option.is-disabled {
    opacity: 0.38;
    pointer-events: none;
}

.practice-status {
    display: flex;
    justify-content: space-between;
    gap: 16px;
    margin: 36px 4px 12px;
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 700;
}

.card-area {
    text-align: center;
}

.kana-card {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    min-height: 420px;
    overflow: hidden;
    background: var(--surface);
    border: 2px solid var(--border-strong);
    border-radius: var(--radius-large);
    box-shadow: var(--shadow);
    outline: none;
}

.kana-card:focus-visible {
    outline: 4px solid rgba(0, 0, 0, 0.16);
    outline-offset: 5px;
}

.kana-panel,
.romaji-panel {
    position: relative;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-width: 0;
    padding: 30px;
    cursor: pointer;
    user-select: none;
    transition: background-color 160ms ease;
}

.kana-panel:hover,
.romaji-panel:hover {
    background: #fafaf8;
}

.kana-panel:first-child {
    border-right: 1px solid var(--border);
}

.romaji-panel {
    grid-column: 1 / -1;
    min-height: 120px;
    border-top: 1px solid var(--border);
}

.kana-label {
    position: absolute;
    top: 20px;
    left: 22px;
    color: var(--text-secondary);
    font-size: 0.76rem;
    font-weight: 700;
    letter-spacing: 0.08em;
}

.kana-character {
    font-size: clamp(6rem, 18vw, 10rem);
    font-weight: 500;
    line-height: 1;
}

.romaji-text {
    font-size: 2.3rem;
    font-weight: 800;
    letter-spacing: 0.05em;
}

.hidden-message {
    display: none;
    color: var(--text-secondary);
    font-size: 0.88rem;
    font-weight: 700;
}

.is-hidden {
    background:
        repeating-linear-gradient(
            -45deg,
            var(--hidden-background),
            var(--hidden-background) 10px,
            #e6e6e2 10px,
            #e6e6e2 20px
        );
}

.is-hidden .kana-character,
.is-hidden .romaji-text {
    display: none;
}

.is-hidden .hidden-message {
    display: block;
}

.is-revealed {
    background: var(--surface);
}

.is-revealed .kana-character,
.is-revealed .romaji-text {
    display: block;
}

.is-revealed .hidden-message {
    display: none;
}

.is-mode-hidden {
    display: none;
}

.kana-card.hiragana-mode,
.kana-card.katakana-mode {
    grid-template-columns: 1fr;
}

.kana-card.hiragana-mode .kana-panel,
.kana-card.katakana-mode .kana-panel {
    border-right: 0;
}

.kana-card.hiragana-mode .romaji-panel,
.kana-card.katakana-mode .romaji-panel {
    grid-column: 1;
}

.card-hint {
    margin: 14px 0 0;
    color: var(--text-secondary);
    font-size: 0.84rem;
}

.navigation {
    display: grid;
    grid-template-columns: 1fr 1.4fr 1fr;
    gap: 12px;
    margin-top: 28px;
}

.primary-button,
.secondary-button {
    min-height: 52px;
    padding: 12px 18px;
    border-radius: var(--radius-medium);
    font-weight: 800;
}

.primary-button {
    background: var(--text-primary);
    border-color: var(--text-primary);
    color: #ffffff;
}

.primary-button:hover {
    transform: translateY(-2px);
}

.secondary-button {
    background: var(--surface);
}

.secondary-button:hover {
    background: var(--button-hover);
}

.extra-actions {
    display: flex;
    justify-content: center;
    gap: 12px;
    margin-top: 18px;
}

.text-button {
    padding: 9px 14px;
    background: transparent;
    border-color: transparent;
    border-radius: 999px;
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 700;
}

.text-button:hover {
    background: var(--button-hover);
    color: var(--text-primary);
}

button:active {
    transform: scale(0.98);
}

@media (max-width: 680px) {
    .kana-app {
        width: min(100% - 24px, 920px);
        padding: 36px 0;
    }

    .button-group,
    .toggle-group {
        grid-template-columns: 1fr;
    }

    .kana-card {
        grid-template-columns: 1fr;
        min-height: auto;
    }

    .kana-panel {
        min-height: 220px;
    }

    .kana-panel:first-child {
        border-right: 0;
        border-bottom: 1px solid var(--border);
    }

    .romaji-panel {
        grid-column: 1;
    }

    .navigation {
        grid-template-columns: 1fr 1fr;
    }

    .primary-button {
        grid-column: 1 / -1;
        grid-row: 1;
    }

    .secondary-button {
        grid-row: 2;
    }

    .extra-actions {
        flex-wrap: wrap;
    }
}