:root {
    --primary: #1b4332;
    --primary-light: #2d6a4f;
    --gold: #d4af37;
    --bg: #f4f6f8;
    --surface: #ffffff;
    --surface-hover: #f8faf9;
    --surface-open: #f3faf5;
    --content-bg: #fdfbf5;
    --card-bg: #ffffff;
    --text-main: #2b2d42;
    --text-strong: #1f2937;
    --text-muted: #6c757d;
    --border: #e9ecef;
    --border-soft: #f0e6d2;
    --num-bg: #e8f5e9;
    --num-border: #c8e6c9;
    --chip-bg: #f1f5f9;
    --chip-text: #475569;
    --target: #d90429;
    --target-bg: #ffeaec;
    --ru: #3b82f6;
    --tr: #10b981;
    --note-bg: #fff3cd;
    --note-text: #856404;
    --header-from: #1b4332;
    --header-to: #081c15;
    --shadow-sm: 0 2px 6px rgba(0,0,0,.05);
    --shadow-md: 0 8px 22px rgba(27,67,50,.10);
    --radius: 14px;
    --ease: cubic-bezier(.4, 0, .2, 1);
    --dur: .32s;
  }
  html[data-theme="dark"] {
    --bg: #0e1513;
    --surface: #16201c;
    --surface-hover: #1b2723;
    --surface-open: #1a2a22;
    --content-bg: #131d19;
    --card-bg: #182421;
    --text-main: #e4ece8;
    --text-strong: #f2f7f5;
    --text-muted: #94a8a0;
    --border: #253430;
    --border-soft: #2b3a34;
    --num-bg: #1f3a2c;
    --num-border: #2c5440;
    --chip-bg: #223029;
    --chip-text: #9ec0ad;
    --target: #ff8da1;
    --target-bg: rgba(255,141,161,.14);
    --ru: #60a5fa;
    --tr: #34d399;
    --note-bg: rgba(212,175,55,.12);
    --note-text: #e2c55f;
    --header-from: #10261d;
    --header-to: #050f0b;
    --gold: #e3c45f;
    --shadow-sm: 0 2px 6px rgba(0,0,0,.35);
    --shadow-md: 0 8px 22px rgba(0,0,0,.45);
  }
  * {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
  }
  html {
    scroll-behavior: smooth;
  }
  body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg);
    color: var(--text-main);
    line-height: 1.5;
    padding-bottom: 60px;
    -webkit-font-smoothing: antialiased;
    transition: background-color .3s var(--ease), color .3s var(--ease);
  }

  /* ---------- Top bar (header + search scroll together) ---------- */
  .topbar {
    position: sticky;
    top: 0;
    z-index: 100;
  }
  header {
    position: relative;
    background: linear-gradient(135deg, var(--header-from) 0%, var(--header-to) 100%);
    color: #fff;
    padding: 22px 16px;
    text-align: center;
    border-bottom: 4px solid var(--gold);
    box-shadow: 0 4px 12px rgba(0,0,0,.15);
    position: relative;
    transition: padding var(--dur) var(--ease);
  }
  header h1 {
    font-size: 1.3rem;
    font-weight: 700;
    margin-bottom: 6px;
    padding: 0 40px; /* keep clear of the theme button */
    letter-spacing: .5px;
    transition: font-size var(--dur) var(--ease), margin var(--dur) var(--ease);
  }
  header p {
    font-size: .85rem;
    color: #b7e4c7;
    max-height: 40px;
    opacity: 1;
    overflow: hidden;
    transition: max-height var(--dur) var(--ease), opacity var(--dur) var(--ease);
  }
  /* the running total is only interesting while searching */
  .topbar.compact:not(.has-query) .search-meta {
    display: none;
  }
  .theme-toggle {
    position: absolute;
    top: 10px;
    right: 10px;
    width: 38px;
    height: 38px;
    border-radius: 50%;
    border: 1px solid rgba(255,255,255,.25);
    background: rgba(255,255,255,.08);
    color: #fff;
    font-size: 1.05rem;
    line-height: 1;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background .2s var(--ease), transform .2s var(--ease);
  }
  .theme-toggle:hover {
    background: rgba(255,255,255,.18);
  }
  .theme-toggle:active {
    transform: scale(.92);
  }

  /* ---------- Search ---------- */
  .search-container {
    padding: 10px 16px;
    background: var(--surface);
    border-bottom: 1px solid var(--border);
    transition: background-color .3s var(--ease), border-color .3s var(--ease);
  }
  .search-box {
    position: relative;
    display: flex;
    align-items: center;
  }
  .search-input {
    width: 100%;
    padding: 10px 38px;
    border-radius: 10px;
    border: 1px solid var(--border);
    background: var(--bg);
    color: var(--text-main);
    font-size: .95rem;
    outline: none;
    transition: border-color .2s var(--ease), box-shadow .2s var(--ease), background-color .3s var(--ease);
  }
  .search-input:focus {
    border-color: var(--primary-light);
    box-shadow: 0 0 0 3px rgba(45,106,79,.15);
  }
  .search-icon {
    position: absolute;
    left: 12px;
    color: var(--text-muted);
    font-size: .95rem;
    pointer-events: none;
  }
  .search-clear {
    position: absolute;
    right: 6px;
    width: 26px;
    height: 26px;
    border: none;
    border-radius: 50%;
    background: var(--chip-bg);
    color: var(--chip-text);
    font-size: 1rem;
    line-height: 1;
    cursor: pointer;
    display: none;
    align-items: center;
    justify-content: center;
  }
  .search-clear.show {
    display: flex;
  }
  .search-meta {
    font-size: .75rem;
    color: var(--text-muted);
    margin-top: 6px;
    min-height: 1em;
  }

  /* ---------- Layout ---------- */
  .container {
    max-width: 680px;
    margin: 16px auto;
    padding: 0 12px;
  }
  .lesson-badge {
    background: var(--primary);
    color: #fff;
    font-weight: 700;
    font-size: .85rem;
    padding: 6px 14px;
    border-radius: 20px;
    display: inline-block;
    margin: 22px 0 10px 4px;
    box-shadow: 0 2px 5px rgba(0,0,0,.12);
  }
  html[data-theme="dark"] .lesson-badge {
    background: var(--primary-light);
  }

  /* ---------- Accordion ---------- */
  .accordion-item {
    position: relative;
    background: var(--surface);
    border-radius: var(--radius);
    margin-bottom: 10px;
    border: 1px solid var(--border);
    overflow: hidden;
    box-shadow: var(--shadow-sm);
    transition: border-color var(--dur) var(--ease),
                box-shadow var(--dur) var(--ease),
                background-color .3s var(--ease);
  }
  .accordion-item::before {
    content: "";
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 4px;
    background: var(--gold);
    transform: scaleX(0);
    transform-origin: left;
    transition: transform var(--dur) var(--ease);
    z-index: 1;
  }
  .accordion-item.active {
    border-color: var(--gold);
    box-shadow: var(--shadow-md);
  }
  .accordion-item.active::before {
    transform: scaleX(1);
  }
  .accordion-header {
    padding: 14px 16px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 10px;
    cursor: pointer;
    user-select: none;
    background: var(--surface);
    -webkit-tap-highlight-color: transparent;
    transition: background-color var(--dur) var(--ease);
  }
  .accordion-header:hover {
    background: var(--surface-hover);
  }
  .accordion-header:focus-visible {
    outline: 2px solid var(--primary-light);
    outline-offset: -2px;
  }
  .accordion-item.active .accordion-header {
    background: var(--surface-open);
  }
  .left-info {
    display: flex;
    align-items: center;
    gap: 12px;
    min-width: 0;
  }
  .num-circle {
    flex: none;
    width: 28px;
    height: 28px;
    border-radius: 50%;
    background: var(--num-bg);
    color: var(--primary);
    font-weight: 700;
    font-size: .8rem;
    display: flex;
    align-items: center;
    justify-content: center;
    border: 1px solid var(--num-border);
    transition: background-color var(--dur) var(--ease),
                color var(--dur) var(--ease),
                border-color var(--dur) var(--ease);
  }
  html[data-theme="dark"] .num-circle {
    color: #a7e8c0;
  }
  .accordion-item.active .num-circle {
    background: var(--primary-light);
    border-color: var(--primary-light);
    color: #fff;
  }
  .word-titles {
    display: flex;
    flex-direction: column;
    min-width: 0;
  }
  .word-tr {
    font-size: .85rem;
    color: var(--text-muted);
  }
  .word-ru {
    font-size: .95rem;
    font-weight: 600;
    color: var(--text-strong);
  }
  .freq-badge {
    font-size: .72rem;
    background: var(--chip-bg);
    color: var(--chip-text);
    padding: 2px 6px;
    border-radius: 4px;
    margin-top: 3px;
    display: inline-block;
    width: fit-content;
  }
  .right-arabic {
    font-family: "Scheherazade New", "Amiri", "Traditional Arabic", serif;
    font-size: 1.85rem;
    line-height: 1.45;
    color: var(--primary);
    font-weight: 600;
    direction: rtl;
    padding-left: 8px;
    white-space: nowrap;
    transition: color var(--dur) var(--ease);
  }
  html[data-theme="dark"] .right-arabic {
    color: #8fd8ab;
  }
  .accordion-item.active .right-arabic {
    color: var(--gold);
  }
  .chevron {
    flex: none;
    width: 9px;
    height: 9px;
    margin: 0 3px 4px 0;
    border-right: 2px solid var(--text-muted);
    border-bottom: 2px solid var(--text-muted);
    transform: rotate(45deg);
    transition: transform var(--dur) var(--ease), border-color var(--dur) var(--ease);
  }
  .accordion-item.active .chevron {
    transform: rotate(-135deg);
    border-right-color: var(--gold);
    border-bottom-color: var(--gold);
  }

  /* Smooth open/close: 0fr -> 1fr animates to the content's natural height */
  .accordion-content {
    display: grid;
    grid-template-rows: 0fr;
    transition: grid-template-rows var(--dur) var(--ease);
  }
  .accordion-item.active .accordion-content {
    grid-template-rows: 1fr;
  }
  .accordion-inner {
    overflow: hidden;
    min-height: 0;
  }
  .accordion-body {
    padding: 16px;
    background: var(--content-bg);
    border-top: 1px solid var(--border-soft);
  }

  /* ---------- Verses ---------- */
  .verse-card {
    background: var(--card-bg);
    border-radius: 10px;
    padding: 14px;
    margin-bottom: 12px;
    border: 1px solid var(--border-soft);
    box-shadow: 0 1px 4px rgba(0,0,0,.03);
  }
  .verse-card:last-child {
    margin-bottom: 0;
  }
  .verse-ref {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 8px;
    font-size: .78rem;
    font-weight: 700;
    color: var(--primary-light);
    margin-bottom: 8px;
    border-bottom: 1px dashed var(--border-soft);
    padding-bottom: 4px;
  }
  html[data-theme="dark"] .verse-ref {
    color: #7fcfa2;
  }
  .verse-arabic {
    font-family: "Scheherazade New", "Amiri", "Traditional Arabic", serif;
    font-size: 1.4rem;
    line-height: 2.1;
    direction: rtl;
    text-align: right;
    color: var(--text-strong);
    margin: 8px 0;
  }
  .verse-arabic .target {
    color: var(--target);
    font-weight: 700;
    background: var(--target-bg);
    padding: 0 4px;
    border-radius: 4px;
  }
  .verse-translations {
    margin-top: 10px;
    font-size: .85rem;
    display: flex;
    flex-direction: column;
    gap: 6px;
  }
  .trans-tr {
    color: var(--text-main);
    border-left: 3px solid var(--tr);
    padding-left: 8px;
  }
  .trans-ru {
    color: var(--text-main);
    border-left: 3px solid var(--ru);
    padding-left: 8px;
  }
  .tag-pill {
    font-size: .7rem;
    font-weight: 600;
    text-transform: uppercase;
    margin-right: 4px;
    color: var(--text-muted);
  }
  .note-box {
    background: var(--note-bg);
    color: var(--note-text);
    padding: 8px 12px;
    border-radius: 6px;
    font-size: .78rem;
    margin-bottom: 10px;
    border-left: 4px solid var(--gold);
  }

  .ar-inline {
    font-family: "Scheherazade New", "Amiri", "Traditional Arabic", serif;
    font-size: 1.2em;
    unicode-bidi: isolate;
  }

  /* ---------- Lesson chips ---------- */
  .lesson-nav {
    display: flex;
    align-items: center;
    padding: 6px 12px 7px 16px;
    background: var(--surface);
    border-bottom: 1px solid var(--border);
  }
  .lesson-chips {
    display: flex;
    gap: 6px;
    flex: 1;
    min-width: 0;
    overflow-x: auto;
    scrollbar-width: none;
    -webkit-overflow-scrolling: touch;
  }
  .lesson-chips::-webkit-scrollbar {
    display: none;
  }
  .nav-actions {
    flex: none;
    display: flex;
    gap: 6px;
    margin-left: 8px;
    padding-left: 8px;
    border-left: 1px solid var(--border);
  }
  .chip {
    flex: none;
    border: 1px solid var(--border);
    background: var(--bg);
    color: var(--text-muted);
    font: inherit;
    font-size: .78rem;
    font-weight: 600;
    padding: 5px 11px;
    border-radius: 999px;
    cursor: pointer;
    white-space: nowrap;
    transition: background-color .2s var(--ease), color .2s var(--ease), border-color .2s var(--ease);
  }
  .chip:hover {
    border-color: var(--primary-light);
    color: var(--primary-light);
  }
  .chip.current {
    background: var(--primary-light);
    border-color: var(--primary-light);
    color: #fff;
  }

  /* ---------- Collapsible lesson ---------- */
  .lesson {
    scroll-margin-top: calc(var(--topbar-h, 150px) + 10px);
  }
  .lesson-head {
    display: flex;
    align-items: center;
    gap: 10px;
    cursor: pointer;
    user-select: none;
    -webkit-tap-highlight-color: transparent;
    padding-right: 6px;
  }
  .lesson-head:focus-visible {
    outline: 2px solid var(--primary-light);
    outline-offset: 2px;
    border-radius: 20px;
  }
  .lesson-head .lesson-badge {
    margin-right: 0;
  }
  .lesson-count {
    font-size: .75rem;
    color: var(--text-muted);
    margin-top: 12px;
  }
  .lesson-chevron {
    margin: 12px 0 0 auto;
  }
  .lesson.collapsed .lesson-chevron {
    transform: rotate(45deg);
  }
  .lesson:not(.collapsed) .lesson-chevron {
    transform: rotate(-135deg);
  }
  .lesson-body {
    display: grid;
    grid-template-rows: 1fr;
    transition: grid-template-rows var(--dur) var(--ease);
  }
  .lesson.collapsed .lesson-body {
    grid-template-rows: 0fr;
  }
  .lesson-inner {
    overflow: hidden;
    min-height: 0;
  }
  #wordsList.searching .lesson-body {
    grid-template-rows: 1fr;
  }

  /* ---------- Empty state & back to top ---------- */
  .no-results {
    display: none;
    text-align: center;
    color: var(--text-muted);
    font-size: .9rem;
    padding: 40px 16px;
  }
  .no-results.show {
    display: block;
  }
  .to-top {
    position: fixed;
    right: 16px;
    bottom: 16px;
    width: 44px;
    height: 44px;
    border-radius: 50%;
    border: none;
    background: var(--primary-light);
    color: #fff;
    font-size: 1.1rem;
    cursor: pointer;
    box-shadow: 0 6px 16px rgba(0,0,0,.25);
    opacity: 0;
    visibility: hidden;
    transform: translateY(12px);
    transition: opacity .25s var(--ease), transform .25s var(--ease), visibility .25s;
    z-index: 90;
  }
  .to-top.show {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
  }

  @media (min-width: 700px) {
    .right-arabic { font-size: 2rem; }
    .verse-arabic { font-size: 1.55rem; }
  }

  @media (prefers-reduced-motion: reduce) {
    html { scroll-behavior: auto; }
    *, *::before, *::after {
      transition-duration: .01ms !important;
      animation-duration: .01ms !important;
    }
  }

  @media print {
    .topbar, .to-top, .chevron { display: none !important; }
    .accordion-content, .lesson-body { grid-template-rows: 1fr !important; }
    .accordion-item { break-inside: avoid; box-shadow: none; }
    body { background: #fff; }
  }
  .load-error {
    text-align: center;
    color: var(--text-muted);
    padding: 40px 16px;
  }

  /* ---------- Progress ---------- */
  .mark {
    flex: none;
    width: 26px;
    height: 26px;
    border-radius: 50%;
    border: 2px solid var(--border);
    background: transparent;
    color: transparent;
    font-size: .78rem;
    line-height: 1;
    cursor: pointer;
    display: grid;
    place-items: center;
    transition: background-color .2s var(--ease), border-color .2s var(--ease), color .2s var(--ease);
  }
  .mark::before {
    content: "✓";
    font-weight: 700;
  }
  .mark:hover {
    border-color: var(--tr);
  }
  .accordion-item.known .mark {
    background: var(--tr);
    border-color: var(--tr);
    color: #fff;
  }
  .accordion-item.known::before {
    background: var(--tr);
    transform: scaleX(1);
  }
  .accordion-item.known .word-ru,
  .accordion-item.known .word-tr {
    opacity: .65;
  }
  .accordion-item.known.active::before {
    background: var(--gold);
  }

  .lesson-progress {
    flex: none;
    width: 46px;
    height: 4px;
    margin-top: 12px;
    border-radius: 2px;
    background: var(--border);
    overflow: hidden;
  }
  .lesson-progress > span {
    display: block;
    height: 100%;
    width: 0;
    background: var(--tr);
    border-radius: 2px;
    transition: width .35s var(--ease);
  }
  .lesson.lesson-done .lesson-badge {
    background: var(--tr);
  }

  .progress-global {
    height: 3px;
    background: var(--border);
  }
  .progress-global > span {
    display: block;
    height: 100%;
    width: 0;
    background: var(--tr);
    transition: width .35s var(--ease);
  }
  .progress-text {
    display: none;
    font-size: .72rem;
    color: var(--text-muted);
    background: var(--surface);
    padding: 6px 16px 7px;
    border-bottom: 1px solid var(--border);
  }
  .progress-text.show {
    display: block;
  }
  .chip-action {
    font-size: .9rem;
    line-height: 1;
    padding: 5px 9px;
  }