:root {
    --bg-color: #0f172a;
    --card-bg: rgba(30, 41, 59, 0.7);
    --accent-color: #38bdf8;
    --accent-hover: #0ea5e9;
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --border-color: rgba(255, 255, 255, 0.1);
    --success-color: #10b981;
    --panel-header: #1e293b;
    --editor-bg: #111827;
}

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

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    overflow: hidden;
    /* Hide body scroll, use app container */
    height: 100vh;
}

.app-container {
    display: flex;
    flex-direction: column;
    height: 100vh;
    background: linear-gradient(rgba(15, 23, 42, 0.8), rgba(15, 23, 42, 0.8)),
        url('background.png');
    background-size: cover;
    background-position: center;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.8rem 1.5rem;
    background: rgba(15, 23, 42, 0.6);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--border-color);
    z-index: 10;
}

.header-main {
    display: flex;
    align-items: center;
    gap: 1.5rem;
}

.back-link {
    text-decoration: none;
    font-size: 0.8rem;
    font-weight: 800;
    color: var(--text-primary);
    background: rgba(255, 255, 255, 0.05);
    padding: 0.5rem 1rem;
    border-radius: 8px;
    border: 1px solid var(--border-color);
    transition: all 0.3s;
}

.back-link:hover {
    background: rgba(255, 255, 255, 0.2);
    transform: scale(1.1);
}

.current-level-info {
    display: flex;
    flex-direction: column;
}

#current-level-label {
    font-size: 0.7rem;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: var(--accent-color);
    font-weight: 800;
}

#current-level-title {
    font-size: 1.1rem;
    font-family: 'Outfit', sans-serif;
    color: var(--text-primary);
}

.step-progress-container {
    display: flex;
    align-items: center;
    gap: 2rem;
}

.step-dots {
    display: flex;
    gap: 0.8rem;
}

.dot {
    width: 12px;
    height: 12px;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.1);
    border: 1px solid var(--border-color);
    transition: all 0.3s;
}

.dot.active {
    background: var(--accent-color);
    box-shadow: 0 0 10px var(--accent-color);
    transform: scale(1.2);
}

.dot.completed {
    background: var(--success-color);
    border-color: var(--success-color);
}

.progress-details {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    background: rgba(0, 0, 0, 0.2);
    padding: 0.4rem 1rem;
    border-radius: 20px;
    font-size: 0.85rem;
}

main {
    flex: 1;
    display: grid;
    grid-template-columns: 350px 1fr 1fr;
    gap: 1px;
    background: var(--border-color);
    overflow: hidden;
}

.instructions-panel,
.editor-panel,
.preview-panel {
    background: var(--bg-color);
    display: flex;
    flex-direction: column;
}

.instructions-panel {
    padding: 0;
    overflow: hidden;
    position: relative;
}

.instructions-content {
    flex: 1;
    overflow-y: auto;
    padding: 1.5rem;
}

.instructions-footer {
    padding: 1rem 1.5rem;
    background: rgba(15, 23, 42, 0.95);
    border-top: 1px solid var(--border-color);
    backdrop-filter: blur(10px);
    flex-shrink: 0;
}

.card {
    background: var(--card-bg);
    border-radius: 16px;
    padding: 1.5rem;
    border: 1px solid var(--border-color);
    backdrop-filter: blur(8px);
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.card h2 {
    font-family: 'Outfit', sans-serif;
    font-size: 1.25rem;
}

.card p {
    color: var(--text-secondary);
    font-size: 0.95rem;
    line-height: 1.6;
}

.learning-points {
    background: rgba(56, 189, 248, 0.05);
    border-left: 4px solid var(--accent-color);
    padding: 0.8rem 1rem;
    border-radius: 4px;
    margin-bottom: 0.5rem;
}

.learning-points h4 {
    font-size: 0.75rem;
    color: var(--accent-color);
    text-transform: uppercase;
    margin-bottom: 0.4rem;
}

.learning-points ul {
    list-style: none;
    font-size: 0.85rem;
    color: var(--text-primary);
}

.learning-points li {
    position: relative;
    padding-left: 1.2rem;
    margin-bottom: 0.2rem;
}

.learning-points li::before {
    content: "💡";
    position: absolute;
    left: 0;
    font-size: 0.8rem;
}

.understand-btn {
    width: 100%;
    padding: 0.8rem;
    background: rgba(56, 189, 248, 0.1);
    border: 1px solid var(--accent-color);
    color: var(--accent-color);
    border-radius: 8px;
    font-weight: 700;
    cursor: pointer;
    transition: all 0.3s;
    margin-bottom: 1rem;
}

.understand-btn:hover {
    background: var(--accent-color);
    color: #000;
}

.understand-btn.hidden {
    display: none;
}

.review-btn {
    width: 100%;
    padding: 0.6rem;
    background: transparent;
    border: 1px dashed var(--accent-color);
    color: var(--accent-color);
    border-radius: 8px;
    font-size: 0.9rem;
    cursor: pointer;
    margin-bottom: 1rem;
    transition: all 0.3s;
}

.review-btn:hover {
    background: rgba(56, 189, 248, 0.1);
}

.review-btn.hidden {
    display: none;
}

.learning-points.hidden {
    display: none;
}

.panel-lock {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(15, 23, 42, 0.8);
    backdrop-filter: blur(4px);
    z-index: 50;
    display: flex;
    justify-content: center;
    align-items: center;
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 600;
    transition: opacity 0.3s;
}

.panel-lock.hidden {
    opacity: 0;
    pointer-events: none;
}

.requirements-card {
    background: rgba(15, 23, 42, 0.6);
    border: 1px solid var(--accent-color);
    border-radius: 16px;
    padding: 1.2rem;
    margin-top: 1.5rem;
}

.req-header {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-bottom: 1rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid var(--border-color);
}

.req-icon {
    font-size: 1.2rem;
}

.requirements-card h3 {
    font-size: 0.95rem;
    color: var(--text-primary);
    font-family: 'Outfit', sans-serif;
}

.requirements-list {
    list-style: none;
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.requirements-list li {
    margin-bottom: 0.6rem;
    display: flex;
    align-items: baseline;
    gap: 0.5rem;
}

.requirements-list li::before {
    content: "✓";
    color: var(--success-color);
    font-weight: bold;
}

.primary-btn {
    width: 100%;
    padding: 1rem;
    font-size: 1rem;
    background: linear-gradient(135deg, var(--accent-color), #3b82f6);
    border: none;
    border-radius: 12px;
    color: #fff;
    font-weight: 800;
    cursor: pointer;
    box-shadow: 0 4px 15px rgba(56, 189, 248, 0.3);
    transition: all 0.3s;
}

.primary-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 25px rgba(56, 189, 248, 0.5);
    filter: brightness(1.1);
}

.primary-btn:active {
    transform: translateY(0);
}

.prev-btn {
    width: 100%;
    padding: 0.8rem;
    font-size: 0.9rem;
    background: rgba(255, 255, 255, 0.05);
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
    border-radius: 12px;
    font-weight: 700;
    cursor: pointer;
    margin-bottom: 0.8rem;
    transition: all 0.3s;
}

.prev-btn:hover {
    background: rgba(255, 255, 255, 0.1);
    color: var(--text-primary);
}

.prev-btn.hidden {
    display: none;
}

.panel-header {
    background: var(--panel-header);
    padding: 0 0.5rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-secondary);
    border-bottom: 1px solid var(--border-color);
    height: 36px;
}

.file-tabs {
    display: flex;
    height: 100%;
}

.file-tab {
    background: transparent;
    border: none;
    padding: 0 1rem;
    color: var(--text-secondary);
    font-size: 0.8rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s;
    height: 100%;
    display: flex;
    align-items: center;
    border-bottom: 2px solid transparent;
}

.file-tab.active {
    color: var(--accent-color);
    border-bottom: 2px solid var(--accent-color);
    background: rgba(56, 189, 248, 0.05);
}

.file-tab:hover:not(.active) {
    background: rgba(255, 255, 255, 0.05);
    color: var(--text-primary);
}

#css-tab.hidden {
    display: none;
}

.code-editor-wrapper {
    flex: 1;
    position: relative;
    background: var(--editor-bg);
    display: flex;
    overflow: hidden;
    /* Scroll is handled inside */
}

.editor-scroll-container {
    flex: 1;
    overflow-y: auto;
    display: flex;
    flex-direction: column;
    position: relative;
    height: 100%;
}

.line-numbers {
    width: 40px;
    padding: 1rem 0;
    text-align: center;
    color: #4b5563;
    font-family: 'Fira Code', monospace;
    font-size: 0.9rem;
    line-height: 1.5;
    /* Match editor line-height */
    border-right: 1px solid var(--border-color);
    user-select: none;
    overflow: hidden;
    /* Scroll synced via JS */
}

.code-prefix,
.code-suffix {
    font-family: 'Fira Code', monospace;
    font-size: 0.95rem;
    line-height: 1.5;
    color: rgba(255, 255, 255, 0.3);
    margin: 0;
    white-space: pre-wrap;
    user-select: none;
}

.code-prefix {
    padding: 1rem 1rem 0 1rem;
}

.code-suffix {
    padding: 0 1rem 1rem 1rem;
}

#code-editor {
    flex: 1;
    background: transparent;
    border: none;
    outline: none;
    color: #e5e7eb;
    font-family: 'Fira Code', monospace;
    font-size: 0.95rem;
    padding: 0 1rem 1rem 1rem;
    /* Bottom padding only */
    line-height: 1.5;
    resize: none;
    overflow: hidden;
    /* Auto-grow handles height */
    min-height: 50px;
    display: block;
}

.preview-window {
    flex: 1;
    background: white;
    margin: 1.5rem;
    border-radius: 8px;
    overflow: hidden;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.3);
    position: relative;
}

#preview-frame {
    width: 100%;
    height: 100%;
    border: none;
    background: white;
}

#refresh-preview {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    font-size: 1rem;
}

/* Modal */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.8);
    backdrop-filter: blur(5px);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 100;
    transition: opacity 0.3s;
}

.modal.hidden {
    opacity: 0;
    pointer-events: none;
}

.modal-content {
    background: var(--card-bg);
    padding: 3rem;
    border-radius: 24px;
    text-align: center;
    border: 1px solid var(--accent-color);
    max-width: 400px;
    width: 90%;
    animation: slideUp 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.success-icon {
    font-size: 4rem;
    margin-bottom: 1rem;
}

@keyframes slideUp {
    from {
        transform: translateY(50px);
        opacity: 0;
    }

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

footer {
    padding: 0.5rem 2rem;
    background: rgba(15, 23, 42, 0.9);
    text-align: center;
    font-size: 0.75rem;
    color: var(--text-secondary);
    border-top: 1px solid var(--border-color);
}

@media (max-width: 1024px) {
    main {
        grid-template-columns: 1fr;
        grid-template-rows: auto minmax(300px, 1fr) 1fr;
        overflow-y: auto;
        gap: 1rem;
        padding-bottom: 2rem;
    }

    body {
        overflow: auto;
        height: auto;
    }

    .app-container {
        height: auto;
        min-height: 100vh;
        display: block;
    }

    header {
        position: sticky;
        top: 0;
    }

    .instructions-panel {
        max-height: 40vh;
        overflow-y: auto;
        border-bottom: 1px solid var(--border-color);
        order: 1;
    }

    .editor-panel {
        order: 2;
        min-height: 400px;
        border-top: 1px solid var(--border-color);
        border-bottom: 1px solid var(--border-color);
    }

    .preview-panel {
        order: 3;
        min-height: 400px;
    }

    .preview-window {
        margin: 0 1rem 1rem;
        height: 400px;
    }
}

@media (max-width: 768px) {
    header {
        padding: 0.8rem 1rem;
    }

    .header-main {
        gap: 0.8rem;
    }

    #current-level-title {
        font-size: 0.9rem;
        max-width: 150px;
        white-space: nowrap;
        overflow: hidden;
        text-overflow: ellipsis;
    }

    .progress-details {
        display: none;
    }

    .instructions-panel {
        max-height: 35vh;
    }

    .editor-panel {
        min-height: 350px;
    }

    .code-editor-wrapper {
        font-size: 0.85rem;
    }

    .line-numbers {
        width: 30px;
        font-size: 0.85rem;
    }
}