:root {
    --bg-primary: #0F1419;
    --bg-secondary: #151C23;
    --bg-tertiary: #18212B;
    --bg-input: #18212B;
    --bg-card: #18212B;
    --bg-hover: #1E2A36;
    --bg-deep: #0A0E12;
    --text-primary: #E6EDF3;
    --text-secondary: #A9B4C0;
    --text-muted: #7E8A97;
    --accent: #2AABEE;
    --accent-hover: #229ED9;
    --border: #243140;
    --border-light: #2C3A4A;
    --danger: #FF453A;
    --danger-bg: #2D1418;
    --success: #2ECC71;
    --warning: #F5A623;
    --radius: 8px;
    --radius-sm: 4px;
    --shadow: 0 4px 24px rgba(0,0,0,0.4);
    --transition: 0.2s ease;
    --sidebar-width: 300px;
    --login-bg: #FFFFFF;
    --login-box-bg: #FFFFFF;
    --login-input-bg: #FFFFFF;
    --login-input-border: #E6EAF0;
    --login-text: #0B0F14;
    --login-sub: #6D7885;
}

[data-theme="day"] {
    --bg-primary: #FFFFFF;
    --bg-secondary: #F6F7F8;
    --bg-tertiary: #EEF0F2;
    --bg-input: #FFFFFF;
    --bg-card: #FFFFFF;
    --bg-hover: #E8EBED;
    --bg-deep: #EEF0F2;
    --text-primary: #0B0F14;
    --text-secondary: #6D7885;
    --text-muted: #98A2AE;
    --accent: #2AABEE;
    --accent-hover: #229ED9;
    --border: #E6EAF0;
    --border-light: #EEF0F2;
    --danger: #FF3B30;
    --danger-bg: #FFF0F0;
    --success: #2ECC71;
    --warning: #F5A623;
    --shadow: 0 4px 24px rgba(0,0,0,0.06);
    --login-bg: #FFFFFF;
    --login-box-bg: #FFFFFF;
    --login-input-bg: #FFFFFF;
    --login-input-border: #E6EAF0;
    --login-text: #0B0F14;
    --login-sub: #6D7885;
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html, body { height: 100%; }
body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.topbar {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 8px 16px;
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    z-index: 100;
    flex-shrink: 0;
}
.topbar-btn {
    background: none;
    border: 1px solid var(--border);
    color: var(--text-primary);
    font-size: 20px;
    width: 36px;
    height: 36px;
    border-radius: var(--radius-sm);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background var(--transition);
}
.topbar-btn:hover { background: var(--bg-tertiary); }
.topbar-title {
    font-size: 16px;
    font-weight: 600;
    color: var(--accent);
    flex: 1;
}
.topbar-right {
    display: flex;
    align-items: center;
    gap: 8px;
}
.topbar-link {
    padding: 6px 14px;
    font-size: 12px;
    color: var(--text-secondary);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    background: none;
    cursor: pointer;
    text-decoration: none;
    transition: background var(--transition);
}
.topbar-link:hover { background: var(--bg-tertiary); }
.topbar-logout {
    padding: 6px 14px;
    font-size: 12px;
    color: var(--danger);
    border: 1px solid rgba(255,107,107,0.3);
    border-radius: var(--radius-sm);
    text-decoration: none;
    transition: background var(--transition);
}
.topbar-logout:hover { background: var(--danger-bg); }

.app {
    display: flex;
    flex: 1;
    overflow: hidden;
    position: relative;
}

.sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.5);
    z-index: 199;
}

.sidebar {
    width: var(--sidebar-width);
    min-width: 220px;
    max-width: 600px;
    background: var(--bg-secondary);
    border-right: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    z-index: 200;
    transition: margin-left 0.3s ease, transform 0.3s ease;
    flex-shrink: 0;
    overflow: hidden;
}
.sidebar.collapsed {
    margin-left: calc(-1 * var(--sidebar-width));
}

.resize-handle {
    width: 5px;
    cursor: col-resize;
    background: var(--border);
    flex-shrink: 0;
    transition: background 0.15s;
    z-index: 201;
}
.resize-handle:hover, .resize-handle.active {
    background: var(--accent);
}

.tree {
    flex: 1;
    overflow-y: auto;
    padding: 8px;
}
.tree-node { user-select: none; }
.tree-label {
    display: flex;
    align-items: center;
    gap: 4px;
    padding: 5px 8px;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 13px;
    white-space: nowrap;
    transition: background var(--transition);
}
.tree-label:hover { background: var(--bg-tertiary); }
.tree-label.active { background: var(--accent); color: #fff; }
.tree-label.active .tree-arrow { color: #fff; }
.tree-label.section-active { background: rgba(233,69,96,0.15); }

.tree-arrow {
    font-size: 10px;
    width: 16px;
    text-align: center;
    color: var(--text-muted);
    flex-shrink: 0;
    transition: transform 0.2s ease;
}
.tree-arrow.open { transform: rotate(90deg); }
.tree-icon {
    font-size: 14px;
    width: 20px;
    text-align: center;
    flex-shrink: 0;
}
.exercise-icon {
    color: var(--accent);
    display: inline-flex;
    align-items: center;
    justify-content: center;
}
.exercise-icon svg {
    display: block;
}
.tree-name {
    flex: 1;
    overflow: hidden;
    text-overflow: ellipsis;
}

.tree-children {
    margin-left: 12px;
    overflow: hidden;
    max-height: 0;
    transition: max-height 0.3s ease;
}
.tree-children.open { max-height: 9999px; }

.main {
    flex: 1;
    overflow-y: auto;
    padding: 20px 24px;
    display: flex;
    flex-direction: column;
}

.breadcrumbs {
    display: flex;
    align-items: center;
    gap: 4px;
    font-size: 13px;
    color: var(--text-muted);
    margin-bottom: 16px;
    flex-wrap: wrap;
    min-height: 20px;
}
.breadcrumbs a {
    color: var(--accent);
    text-decoration: none;
    cursor: pointer;
    transition: opacity var(--transition);
}
.breadcrumbs a:hover { opacity: 0.8; }
.breadcrumbs .sep { color: var(--text-muted); margin: 0 2px; }
.breadcrumbs .current { color: var(--text-primary); font-weight: 500; }

.placeholder {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
}
.placeholder-inner { text-align: center; color: var(--text-muted); }
.placeholder-icon { font-size: 48px; margin-bottom: 12px; }
.placeholder-inner p { font-size: 16px; }

.section-panel, .admin-panel { max-width: 900px; width: 100%; }
.section-panel-header {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 20px;
    flex-wrap: wrap;
}
.section-panel-header h2 { font-size: 22px; color: var(--accent); }
.section-panel-actions { display: flex; gap: 8px; flex-wrap: wrap; }

.section-contents {}
.section-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 14px 16px;
    background: var(--bg-card);
    border-radius: var(--radius);
    margin-bottom: 8px;
    cursor: pointer;
    transition: background var(--transition), transform 0.1s;
}
.section-item:hover { background: var(--bg-hover); transform: translateX(2px); }
.section-item-icon { font-size: 24px; flex-shrink: 0; }
.section-item-info { flex: 1; min-width: 0; }
.section-item-name { font-size: 15px; font-weight: 500; }
.section-item-type { font-size: 12px; color: var(--text-muted); }

.exercise-panel { max-width: 900px; width: 100%; }
.exercise-header {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 20px;
    flex-wrap: wrap;
}
.exercise-header h2 { font-size: 22px; color: var(--accent); flex: 1; min-width: 0; }
.exercise-actions-bar { display: flex; gap: 8px; }
.btn-sm {
    padding: 5px 12px;
    font-size: 12px;
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    background: var(--bg-secondary);
    color: var(--text-secondary);
    cursor: pointer;
    transition: background var(--transition);
    white-space: nowrap;
}
.btn-sm:hover { background: var(--bg-tertiary); }
.btn-danger { border-color: rgba(255,107,107,0.3); color: var(--danger); }
.btn-danger:hover { background: var(--danger-bg); }

.section-block { margin-bottom: 20px; }
.section-block h3 {
    font-size: 12px;
    color: var(--text-muted);
    margin-bottom: 8px;
    text-transform: uppercase;
    letter-spacing: 1px;
    font-weight: 600;
}
textarea, input[type="text"], input[type="password"] {
    width: 100%;
    padding: 10px 12px;
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    color: var(--text-primary);
    font-family: inherit;
    font-size: 14px;
    resize: vertical;
    outline: none;
    transition: border-color var(--transition);
    margin-bottom: 8px;
}
textarea:focus, input[type="text"]:focus, input[type="password"]:focus { border-color: var(--accent); }
textarea::placeholder, input::placeholder { color: var(--text-muted); }

.edit-btn {
    margin-top: 4px;
    padding: 8px 20px;
    background: var(--accent);
    color: #fff;
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 13px;
    font-weight: 500;
    transition: background var(--transition);
}
.edit-btn:hover { background: var(--accent-hover); }

.file-list { margin-bottom: 12px; }
.file-card {
    display: flex;
    gap: 12px;
    padding: 10px 12px;
    background: var(--bg-card);
    border-radius: var(--radius);
    margin-bottom: 8px;
    align-items: flex-start;
}
.file-thumb {
    width: 80px;
    height: 60px;
    border-radius: var(--radius-sm);
    overflow: hidden;
    background: var(--bg-deep);
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
}
.file-thumb video, .file-thumb img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}
.file-thumb .file-type-icon {
    font-size: 28px;
    color: var(--text-muted);
}
.file-info { flex: 1; min-width: 0; }
.file-name {
    font-size: 13px;
    font-weight: 500;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
    margin-bottom: 4px;
}
.file-meta {
    font-size: 11px;
    color: var(--text-muted);
    margin-bottom: 6px;
}
.file-description {
    font-size: 12px;
    color: var(--text-secondary);
    margin-bottom: 6px;
    padding: 4px 8px;
    background: var(--bg-deep);
    border-radius: var(--radius-sm);
    min-height: 20px;
}
.file-description.empty {
    color: var(--text-muted);
    font-style: italic;
}
.file-desc-edit {
    display: flex;
    gap: 6px;
    margin-bottom: 6px;
}
.file-desc-edit input {
    flex: 1;
    margin-bottom: 0;
    padding: 6px 8px;
    font-size: 12px;
}
.file-desc-edit button {
    padding: 4px 10px;
    font-size: 11px;
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    background: var(--accent);
    color: #fff;
    cursor: pointer;
}
.file-desc-edit button.cancel-btn {
    background: none;
    color: var(--text-secondary);
}
.file-actions { display: flex; gap: 6px; flex-wrap: wrap; }
.file-actions button {
    padding: 4px 10px;
    font-size: 11px;
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    background: none;
    color: var(--text-secondary);
    cursor: pointer;
    transition: background var(--transition);
}
.file-actions button:hover { background: rgba(255,255,255,0.08); }
.file-actions .btn-del { border-color: rgba(255,107,107,0.3); color: var(--danger); }
.file-actions .btn-del:hover { background: var(--danger-bg); }

.upload-area {
    display: flex;
    gap: 8px;
    align-items: flex-start;
    flex-wrap: wrap;
}
.file-input-label {
    display: inline-flex;
    align-items: center;
    padding: 8px 20px;
    background: var(--bg-tertiary);
    color: var(--text-primary);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 13px;
    font-weight: 500;
    transition: background var(--transition);
}
.file-input-label:hover { background: var(--bg-hover); }
.file-input-label input[type="file"] {
    position: absolute;
    width: 1px;
    height: 1px;
    overflow: hidden;
    clip: rect(0,0,0,0);
    white-space: nowrap;
    border: 0;
}
.selected-files {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
    align-items: center;
}
.selected-file-item {
    display: inline-block;
    padding: 4px 10px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    font-size: 12px;
    color: var(--text-secondary);
    max-width: 200px;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}
.upload-btn {
    padding: 8px 20px;
    background: var(--accent);
    color: #fff;
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 13px;
    font-weight: 500;
    transition: background var(--transition);
}
.upload-btn:hover { background: var(--accent-hover); }

.fab {
    position: fixed;
    bottom: 24px;
    right: 24px;
    width: 56px;
    height: 56px;
    border-radius: 50%;
    background: var(--accent);
    color: #fff;
    font-size: 28px;
    border: none;
    cursor: pointer;
    box-shadow: 0 4px 16px rgba(233,69,96,0.4);
    z-index: 300;
    transition: transform 0.2s, background 0.2s;
    display: flex;
    align-items: center;
    justify-content: center;
}
.fab:hover { background: var(--accent-hover); transform: scale(1.05); }
.fab.open { transform: rotate(45deg); }

.fab-menu {
    position: fixed;
    bottom: 88px;
    right: 24px;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    z-index: 301;
    overflow: hidden;
}
.fab-menu button {
    display: block;
    width: 100%;
    padding: 12px 20px;
    background: none;
    border: none;
    border-bottom: 1px solid var(--border);
    color: var(--text-primary);
    font-size: 14px;
    cursor: pointer;
    text-align: left;
    white-space: nowrap;
    transition: background var(--transition);
}
.fab-menu button:last-child { border-bottom: none; }
.fab-menu button:hover { background: var(--bg-tertiary); }

.modal {
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.85);
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 24px;
}
.modal-content {
    max-width: 95vw;
    max-height: 90vh;
    display: flex;
    align-items: center;
    justify-content: center;
}
.modal-content video { max-width: 90vw; max-height: 85vh; border-radius: var(--radius); }
.modal-content img { max-width: 90vw; max-height: 85vh; border-radius: var(--radius); object-fit: contain; }
.modal-close {
    position: fixed;
    top: 16px;
    right: 20px;
    font-size: 32px;
    color: #fff;
    background: none;
    border: none;
    cursor: pointer;
    z-index: 1001;
    line-height: 1;
}

.settings-modal-overlay {
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.6);
    z-index: 500;
    display: flex;
    align-items: center;
    justify-content: center;
}
.settings-modal {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
    width: 400px;
    max-width: 95vw;
    box-shadow: var(--shadow);
}
.settings-modal h3 {
    margin-bottom: 16px;
    color: var(--accent);
    font-size: 18px;
}
.settings-actions {
    display: flex;
    gap: 8px;
    margin-top: 8px;
}

.settings-menu-list {
    display: flex;
    flex-direction: column;
    gap: 4px;
    margin-bottom: 16px;
}
.settings-menu-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 14px 16px;
    background: var(--bg-primary);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    cursor: pointer;
    transition: background var(--transition), border-color var(--transition);
    text-align: left;
    width: 100%;
    color: var(--text-primary);
    font-size: 14px;
}
.settings-menu-item:hover {
    background: var(--bg-secondary);
    border-color: var(--text-muted);
}
.settings-menu-icon {
    font-size: 18px;
    width: 24px;
    text-align: center;
    flex-shrink: 0;
}
.settings-menu-text {
    flex: 1;
    font-weight: 500;
}
.settings-menu-arrow {
    color: var(--text-muted);
    font-size: 20px;
    font-weight: 300;
}
.settings-page-header {
    display: flex;
    align-items: center;
    gap: 8px;
    margin-bottom: 16px;
}
.settings-page-header h3 {
    margin-bottom: 0;
}
.settings-back-btn {
    background: none;
    border: none;
    color: var(--accent);
    font-size: 22px;
    cursor: pointer;
    padding: 0 4px;
    line-height: 1;
    transition: opacity var(--transition);
}
.settings-back-btn:hover {
    opacity: 0.7;
}

.theme-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 10px;
    margin-bottom: 12px;
}
.theme-card {
    padding: 12px;
    border: 2px solid var(--border);
    border-radius: var(--radius);
    cursor: pointer;
    transition: border-color var(--transition), transform 0.1s;
    text-align: center;
}
.theme-card:hover { transform: translateY(-1px); border-color: var(--text-muted); }
.theme-card.active { border-color: var(--accent); }
.theme-card-preview {
    height: 40px;
    border-radius: var(--radius-sm);
    margin-bottom: 8px;
    display: flex;
    overflow: hidden;
}
.theme-card-preview > div { flex: 1; }
.theme-card-name {
    font-size: 13px;
    font-weight: 500;
    color: var(--text-primary);
}

.admin-panel { }
.admin-user-list { margin-bottom: 20px; }
.admin-user-row {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 12px 16px;
    background: var(--bg-card);
    border-radius: var(--radius);
    margin-bottom: 8px;
    flex-wrap: wrap;
}
.admin-user-login {
    font-size: 15px;
    font-weight: 500;
    min-width: 100px;
}
.admin-user-flags {
    display: flex;
    gap: 8px;
    align-items: center;
    flex: 1;
}
.admin-user-flags span {
    font-size: 11px;
    padding: 2px 8px;
    border-radius: 10px;
    background: var(--bg-tertiary);
    color: var(--text-secondary);
}
.admin-user-flags span.role-admin {
    background: rgba(233,69,96,0.2);
    color: var(--accent);
}
.admin-user-flags span.role-editor {
    background: rgba(78,205,196,0.2);
    color: var(--success);
}
.admin-user-actions {
    display: flex;
    gap: 6px;
}
.admin-add-user {
    background: var(--bg-card);
    padding: 16px;
    border-radius: var(--radius);
}
.admin-add-user h3 {
    font-size: 14px;
    color: var(--text-muted);
    margin-bottom: 12px;
    text-transform: uppercase;
    letter-spacing: 1px;
}
.admin-form {
    display: flex;
    flex-direction: column;
    gap: 8px;
}
.checkbox-label {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 13px;
    color: var(--text-secondary);
    cursor: pointer;
}
.checkbox-label input { accent-color: var(--accent); }

@media (max-width: 900px) {
    .sidebar {
        position: fixed;
        top: 0;
        left: 0;
        bottom: 0;
        transform: translateX(-100%);
        margin-left: 0 !important;
        box-shadow: var(--shadow);
        z-index: 200;
        width: 280px !important;
        min-width: 280px !important;
    }
    .sidebar.mobile-open {
        transform: translateX(0);
    }
    .sidebar-overlay.visible {
        display: block;
    }
    .resize-handle { display: none; }
    .main { padding: 16px; }
    .exercise-header { gap: 8px; }
    .exercise-header h2 { font-size: 18px; }
    .file-card { flex-direction: column; }
    .file-thumb { width: 100%; height: 120px; }
    .fab { bottom: 16px; right: 16px; }
    .fab-menu { bottom: 80px; right: 16px; }
}

@media (min-width: 901px) {
    .sidebar-overlay { display: none !important; }
}