:root {
    --bg-color: #0f172a;
    --card-bg: #1e293b;
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --accent: #f59e0b;
    /* Amber/Gold */
    --accent-hover: #d97706;
    --danger: #ef4444;
    --success: #10b981;
    --glass-bg: rgba(30, 41, 59, 0.7);
    --glass-border: rgba(255, 255, 255, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
    font-family: 'Inter', 'Noto Sans KR', 'Noto Sans SC', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.5;
    overflow-x: hidden;
    min-height: 100vh;
}

.app-container {
    max-width: 1000px;
    margin: 0 auto;
    padding: 2rem;
    padding-top: 6rem;
}

/* Navbar */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 100;
    background: var(--glass-bg);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--glass-border);
    padding: 1rem 0;
}

.nav-content {
    max-width: 1000px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 2rem;
}

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    letter-spacing: -0.025em;
}

.logo span {
    color: var(--accent);
}

.nav-links {
    display: flex;
    gap: 1rem;
}

.nav-btn {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 1rem;
    border-radius: 0.5rem;
    cursor: pointer;
    font-weight: 600;
    transition: var(--transition);
}

.nav-btn i {
    width: 18px;
    height: 18px;
}

.nav-btn:hover {
    color: var(--text-primary);
    background: rgba(255, 255, 255, 0.05);
}

.nav-btn.active {
    color: var(--accent);
    background: rgba(245, 158, 11, 0.1);
}

/* Views */
.view {
    display: none;
    animation: fadeIn 0.4s ease-out;
}

.view.active {
    display: block;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Study View */
.study-stats {
    display: flex;
    justify-content: center;
    margin-bottom: 2rem;
}

.stat-item {
    text-align: center;
    background: var(--card-bg);
    padding: 1rem 2rem;
    border-radius: 1rem;
    border: 1px solid var(--glass-border);
    box-shadow: var(--shadow-lg);
}

.stat-item .label {
    display: block;
    font-size: 0.875rem;
    color: var(--text-secondary);
    margin-bottom: 0.25rem;
}

.stat-item .value {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--accent);
}

/* Flashcard */
.card-container {
    max-width: 500px;
    margin: 0 auto;
    min-height: 400px;
    cursor: pointer;
}

.flashcard {
    width: 100%;
    min-height: 450px;
    background: var(--card-bg);
    border-radius: 1.5rem;
    border: 1px solid var(--glass-border);
    padding: 2rem;
    box-shadow: var(--shadow-lg);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    transition: var(--transition);
    background: linear-gradient(135deg, #1e293b 0%, #0f172a 100%);
    position: relative;
}

.card-content {
    width: 100%;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    flex-grow: 1;
}

.hanzi-wrapper {
    display: flex;
    justify-content: center;
    align-items: center;
    transition: var(--transition);
    flex-grow: 1;
}

.hanzi {
    font-size: 6rem;
    font-weight: 700;
    color: #fff;
    text-shadow: 0 0 30px rgba(255, 255, 255, 0.15);
    text-align: center;
}

.reveal-content {
    display: flex;
    flex-direction: column;
    align-items: center;
    width: 100%;
    transition: all 0.5s cubic-bezier(0.4, 0, 0.2, 1);
    opacity: 1;
    transform: translateY(0);
    margin-top: 1rem;
}

.reveal-content.hidden {
    opacity: 0;
    transform: translateY(20px);
    pointer-events: none;
    height: 0;
    margin: 0;
    overflow: hidden;
}

.hanzi-wrapper.shrunk {
    flex-grow: 0;
    margin-bottom: 1rem;
}

.hanzi-wrapper.shrunk .hanzi {
    font-size: 4rem;
}

.pinyin {
    font-size: 1.75rem;
    color: var(--accent);
    font-weight: 600;
    margin-bottom: 0.5rem;
}

.meaning {
    font-size: 2.25rem;
    font-weight: 600;
    margin-bottom: 2rem;
    text-align: center;
}

.example-box {
    text-align: center;
    background: rgba(255, 255, 255, 0.03);
    padding: 1.5rem;
    border-radius: 1rem;
    width: 100%;
    border: 1px solid rgba(255, 255, 255, 0.05);
}

.example-zh {
    font-size: 1.125rem;
    margin-bottom: 0.25rem;
    color: var(--text-primary);
}

.example-ko {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.hint {
    margin-top: 2rem;
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.hidden {
    display: none !important;
}

/* Study Controls */
.study-controls {
    display: flex;
    justify-content: stretch;
    gap: 0;
    /* Flush buttons like in the image */
    margin-top: 3rem;
    animation: slideUp 0.3s ease-out;
    border-radius: 0.75rem;
    overflow: hidden;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
    box-shadow: var(--shadow-lg);
}

@keyframes slideUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.srs-btn {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 0.75rem 0.5rem;
    border: none;
    cursor: pointer;
    transition: var(--transition);
    color: white;
    flex: 1;
    min-height: 80px;
}

.srs-btn .interval {
    font-size: 0.875rem;
    opacity: 0.9;
    font-weight: 400;
    margin-bottom: 0.25rem;
    min-height: 1.2em;
    /* Keep space even if empty */
}

.srs-btn .label {
    font-size: 1.25rem;
    font-weight: 700;
}

.srs-btn.again {
    background-color: #c62828;
}

/* Dark Red */
.srs-btn.hard {
    background-color: #37474f;
}

/* Dark Blue-Gray */
.srs-btn.good {
    background-color: #2e7d32;
}

/* Dark Green */
.srs-btn.easy {
    background-color: #0277bd;
}

/* Dark Blue */

.srs-btn:hover {
    filter: brightness(1.2);
}

.srs-btn:active {
    transform: scale(0.98);
}

.spin {
    animation: spin 1s linear infinite;
}

@keyframes spin {
    from {
        transform: rotate(0deg);
    }

    to {
        transform: rotate(360deg);
    }
}

/* Table View */
.section-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
}

.btn-primary {
    background: var(--accent);
    color: #000;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: 0.5rem;
    font-weight: 700;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    transition: var(--transition);
}

.btn-primary:hover {
    background: var(--accent-hover);
    transform: translateY(-1px);
}

.card-list-container {
    background: var(--card-bg);
    border-radius: 1rem;
    border: 1px solid var(--glass-border);
    overflow: hidden;
}

.card-table {
    width: 100%;
    border-collapse: collapse;
    text-align: left;
}

.card-table th,
.card-table td {
    padding: 1rem 1.5rem;
    border-bottom: 1px solid var(--glass-border);
}

.card-table th {
    background: rgba(255, 255, 255, 0.02);
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    font-size: 0.75rem;
    letter-spacing: 0.05em;
}

.card-table tr:hover {
    background: rgba(255, 255, 255, 0.01);
}

.btn-icon {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    padding: 0.25rem;
    border-radius: 0.25rem;
    transition: var(--transition);
}

.btn-icon:hover {
    color: var(--text-primary);
    background: rgba(255, 255, 255, 0.05);
}

.btn-icon.delete:hover {
    color: var(--danger);
}

/* Modals */
.modal {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    z-index: 200;
    background: rgba(0, 0, 0, 0.8);
    backdrop-filter: blur(4px);
    align-items: center;
    justify-content: center;
}

.modal.active {
    display: flex;
}

.modal-content {
    background: var(--card-bg);
    width: 90%;
    max-width: 500px;
    padding: 2rem;
    border-radius: 1.5rem;
    border: 1px solid var(--glass-border);
    box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
}

.form-group {
    margin-bottom: 1.25rem;
}

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    color: var(--text-secondary);
}

.form-group input,
.form-group textarea {
    width: 100%;
    background: #0f172a;
    border: 1px solid var(--glass-border);
    border-radius: 0.5rem;
    padding: 0.75rem 1rem;
    color: #fff;
    font-family: inherit;
    transition: var(--transition);
}

.form-group input:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--accent);
    box-shadow: 0 0 0 2px rgba(245, 158, 11, 0.2);
}

.modal-actions {
    display: flex;
    justify-content: flex-end;
    gap: 1rem;
    margin-top: 2rem;
}

.btn-text {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    font-weight: 600;
    cursor: pointer;
    padding: 0.75rem 1rem;
}

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

.btn-secondary {
    background: rgba(255, 255, 255, 0.05);
    color: var(--text-primary);
    border: 1px solid var(--glass-border);
    padding: 0.75rem 1.25rem;
    border-radius: 0.5rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
}

.btn-secondary:hover {
    background: rgba(255, 255, 255, 0.1);
}

.btn-outline-danger {
    background: transparent;
    border: 1px solid var(--danger);
    color: var(--danger);
    padding: 0.75rem 1.25rem;
    border-radius: 0.5rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
}

.btn-outline-danger:hover {
    background: var(--danger);
    color: #fff;
}

.btn-group {
    display: flex;
    gap: 0.75rem;
}

.settings-group {
    background: var(--card-bg);
    border-radius: 1rem;
    padding: 2rem;
    margin-bottom: 2rem;
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--glass-border);
}

.settings-group h3 {
    font-size: 1.25rem;
    margin-bottom: 2rem;
    color: var(--accent);
    font-weight: 700;
}

.settings-item {
    margin-bottom: 1.5rem;
}

.settings-item label {
    display: block;
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.input-with-hint {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

#new-cards-limit {
    background: var(--bg-color);
    border: 1px solid var(--glass-border);
    border-radius: 0.75rem;
    padding: 0.8rem 1.2rem;
    color: var(--text-primary);
    font-size: 1.1rem;
    width: 120px;
    transition: var(--transition);
    outline: none;
}

#new-cards-limit:focus {
    border-color: var(--accent);
    box-shadow: 0 0 0 3px rgba(245, 158, 11, 0.2);
}

.hint {
    font-size: 0.875rem;
    color: var(--text-secondary);
    line-height: 1.5;
}

.danger-zone {
    border-top: 1px solid var(--glass-border);
    padding-top: 2rem;
    margin-top: 1rem;
}

.danger-zone p {
    font-size: 0.9rem;
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
}

/* Responsive */
@media (max-width: 640px) {
    .app-container {
        padding: 1rem;
        padding-top: 5rem;
    }

    .nav-content {
        padding: 0 1rem;
    }

    .nav-btn span {
        display: none;
    }

    .hanzi {
        font-size: 3rem;
    }

    .meaning {
        font-size: 1.5rem;
    }
}