:root {
  --ink: #17202a;
  --muted: #65727d;
  --line: #dce4e8;
  --paper: #fbfcfd;
  --panel: #ffffff;
  --teal: #007f7a;
  --teal-dark: #005f5b;
  --berry: #b7355b;
  --amber: #d7971f;
  --mint: #e7f6f2;
  --rose: #faeef2;
  --blue: #eaf2fb;
  --success: #207a42;
  --danger: #b93030;
  --shadow: 0 18px 45px rgba(23, 32, 42, 0.08);
  font-family:
    Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
    sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    linear-gradient(180deg, rgba(231, 246, 242, 0.9), rgba(251, 252, 253, 0.5) 34rem),
    var(--paper);
  color: var(--ink);
}

button,
input {
  font: inherit;
}

button {
  cursor: pointer;
}

.app-shell {
  width: min(1120px, calc(100% - 32px));
  margin: 0 auto;
  padding: 24px 0 48px;
}

.topbar {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 18px;
  align-items: center;
  min-height: 180px;
  padding: 28px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background:
    linear-gradient(135deg, rgba(255, 255, 255, 0.95), rgba(234, 242, 251, 0.9)),
    var(--panel);
  box-shadow: var(--shadow);
}

.eyebrow,
.subtitle,
.panel-heading p,
.exercise-title p,
.result,
.score-label {
  margin: 0;
  color: var(--muted);
}

.eyebrow {
  font-size: 0.84rem;
  font-weight: 700;
  text-transform: uppercase;
}

h1,
h2,
h3,
h4 {
  margin: 0;
  line-height: 1.1;
  letter-spacing: 0;
}

h1 {
  margin-top: 8px;
  font-size: clamp(2rem, 7vw, 4.8rem);
}

.subtitle {
  margin-top: 8px;
  font-size: clamp(1rem, 2.5vw, 1.35rem);
}

.score-panel {
  display: grid;
  place-items: center;
  width: 118px;
  height: 118px;
  border: 1px solid rgba(0, 127, 122, 0.24);
  border-radius: 8px;
  background: var(--mint);
}

.score-panel strong {
  font-size: 2rem;
}

.tabs {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 8px;
  margin: 16px 0;
}

.tab-button,
.segment,
.primary-button,
.secondary-button,
.ghost-button,
.mark-card-button {
  min-height: 44px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  color: var(--ink);
  font-weight: 700;
}

.tab-button.is-active {
  border-color: var(--teal);
  background: var(--teal);
  color: #fff;
}

.tab-panel {
  display: none;
}

.tab-panel.is-active {
  display: block;
}

.panel-heading {
  display: flex;
  gap: 16px;
  align-items: center;
  justify-content: space-between;
  margin: 22px 0 16px;
}

.panel-heading h2 {
  font-size: clamp(1.45rem, 4vw, 2.25rem);
}

.exercise-block,
.reference-section,
.flashcard-area {
  margin-top: 16px;
  padding: 22px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.92);
  box-shadow: 0 12px 30px rgba(23, 32, 42, 0.05);
}

.exercise-title {
  display: flex;
  gap: 12px;
  align-items: flex-start;
  margin-bottom: 18px;
}

.number-badge {
  display: grid;
  place-items: center;
  flex: 0 0 auto;
  width: 34px;
  height: 34px;
  border-radius: 8px;
  background: var(--rose);
  color: var(--berry);
  font-weight: 800;
}

.grid {
  display: grid;
  gap: 12px;
}

.two-col {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.answer-row,
.flag-row,
.mashup-row,
.inline-answer-row,
.intro-row,
.free-row,
.category-column {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
}

.answer-row {
  display: grid;
  grid-template-columns: minmax(0, 0.78fr) minmax(190px, 1fr);
  gap: 10px;
  align-items: center;
  min-height: 58px;
  padding: 12px;
}

.prompt {
  font-weight: 700;
  overflow-wrap: anywhere;
}

.nowrap-label {
  white-space: nowrap;
}

input[type="text"] {
  width: 100%;
  min-height: 42px;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 9px 10px;
  background: #fff;
}

input[type="text"]:focus,
.tab-button:focus-visible,
.primary-button:focus-visible,
.secondary-button:focus-visible,
.ghost-button:focus-visible,
.mark-card-button:focus-visible,
.char-button:focus-visible,
.segment:focus-visible,
.flashcard:focus-visible,
.drag-chip:focus-visible,
.chain-letter:focus-visible,
.category-drop:focus-visible {
  outline: 3px solid rgba(215, 151, 31, 0.45);
  outline-offset: 2px;
}

.is-correct {
  border-color: rgba(32, 122, 66, 0.5);
  background: #f0fbf3;
}

.is-wrong {
  border-color: rgba(185, 48, 48, 0.45);
  background: #fff3f3;
}

.char-toolbar {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  align-items: center;
  margin: -2px 0 16px;
  color: var(--muted);
  font-size: 0.95rem;
  font-weight: 700;
}

.char-button {
  min-width: 34px;
  min-height: 34px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  color: var(--ink);
  font-weight: 800;
}

.char-button:hover {
  border-color: var(--teal);
  background: var(--mint);
}

.exercise-example {
  display: grid;
  gap: 8px;
  margin: 0 0 16px;
  padding: 12px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
}

.example-heading {
  display: flex;
  gap: 6px;
  align-items: baseline;
}

.example-heading span {
  font-weight: 800;
  text-decoration: underline;
}

.example-heading em {
  color: var(--muted);
}

.answer-line {
  display: inline-block;
  min-width: 22ch;
  border-bottom: 1px solid var(--ink);
}

.flag-example {
  grid-template-columns: max-content max-content minmax(18ch, 1fr);
  align-items: center;
}

.flag-example .example-heading {
  grid-column: 1 / -1;
}

.flag-example img,
.flag-row img {
  width: 86px;
  max-height: 54px;
  border: 1px solid var(--line);
  object-fit: cover;
}

.flag-grid {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.flag-row {
  display: grid;
  grid-template-columns: 92px minmax(0, 1fr);
  gap: 10px;
  align-items: center;
  padding: 12px;
}

.flag-row input {
  grid-column: 1 / -1;
}

.letter-chain {
  display: block;
  margin: 0 0 10px;
  padding: 12px;
  border: 1px solid rgba(0, 127, 122, 0.24);
  border-radius: 8px;
  background: var(--mint);
  font-size: clamp(1rem, 3vw, 1.34rem);
  font-weight: 800;
  letter-spacing: 0.03em;
  overflow-wrap: anywhere;
  user-select: none;
}

.chain-letter {
  display: inline;
  min-height: 0;
  border: 0;
  border-radius: 3px;
  background: transparent;
  color: inherit;
  font: inherit;
  letter-spacing: inherit;
  margin: 0;
  padding: 0;
  touch-action: none;
}

.chain-letter:hover,
.chain-letter.is-marked {
  background: #fff36b;
  box-shadow: 0 0 0 1px #d8bf00 inset;
}

.chain-letter.is-break-after {
  margin-right: 0.3em;
}

.mashup-row {
  display: grid;
  grid-template-columns: max-content minmax(0, 1fr);
  gap: 8px 10px;
  align-items: center;
  padding: 12px;
}

.mashup-row input {
  grid-column: 1 / -1;
}

.mashup-label {
  font-weight: 800;
}

.mashup-text {
  display: block;
  padding: 10px 12px;
  border: 1px solid rgba(0, 127, 122, 0.24);
  border-radius: 8px;
  background: var(--mint);
  font-weight: 800;
  overflow-wrap: anywhere;
}

.number-find-grid {
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

.inline-answer-row {
  display: flex;
  flex-wrap: wrap;
  gap: 7px;
  align-items: center;
  min-height: 58px;
  padding: 12px;
  font-weight: 700;
}

.inline-answer-row input {
  width: min(100%, 16ch);
  flex: 1 1 12ch;
}

.word-bank {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: -4px 0 16px;
}

.drag-chip {
  display: inline-flex;
  align-items: center;
  min-height: 36px;
  padding: 7px 12px;
  border: 1px solid rgba(0, 127, 122, 0.25);
  border-radius: 8px;
  background: var(--mint);
  color: var(--teal-dark);
  font-weight: 800;
  box-shadow: 0 5px 14px rgba(0, 95, 91, 0.08);
}

.drag-chip:hover,
.drag-chip.is-selected {
  border-color: var(--teal-dark);
  background: var(--teal-dark);
  color: #fff;
}

.category-board {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 10px;
}

.category-column {
  display: grid;
  gap: 10px;
  padding: 12px;
}

.category-column h4 {
  color: var(--teal-dark);
}

.category-drop {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  align-content: flex-start;
  min-height: 150px;
  padding: 8px;
  border: 1px dashed rgba(0, 127, 122, 0.45);
  border-radius: 8px;
  background: #fff;
}

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

.intro-row {
  display: flex;
  flex-wrap: wrap;
  gap: 7px;
  align-items: center;
  min-height: 56px;
  padding: 12px;
  font-weight: 700;
}

.intro-row input {
  width: min(100%, 24ch);
  flex: 1 1 16ch;
}

.free-row {
  display: grid;
  grid-template-columns: 110px minmax(210px, 1fr) minmax(240px, 1fr);
  gap: 8px 12px;
  align-items: center;
  padding: 10px;
}

.free-prompt {
  color: var(--muted);
  font-weight: 800;
}

.example-answer {
  display: none;
  margin: 0;
  color: var(--teal-dark);
  font-weight: 700;
}

.example-answer.is-visible {
  display: block;
}

.example-line {
  margin: 0 0 14px;
}

.actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: center;
  margin-top: 16px;
}

.primary-button {
  border-color: var(--teal);
  background: var(--teal);
  color: #fff;
  padding: 0 18px;
}

.primary-button:hover {
  background: var(--teal-dark);
}

.secondary-button,
.ghost-button,
.mark-card-button {
  padding: 0 16px;
}

.secondary-button:hover,
.ghost-button:hover,
.segment:hover {
  border-color: var(--teal);
}

.result {
  font-weight: 700;
}

.result.good {
  color: var(--success);
}

.result.needs-work {
  color: var(--danger);
}

.segmented {
  display: inline-flex;
  flex-wrap: wrap;
  gap: 6px;
  padding: 4px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
}

.segment {
  min-height: 38px;
  border-color: transparent;
  padding: 0 12px;
}

.segment.is-active {
  background: var(--berry);
  color: #fff;
}

.flashcard-area {
  display: grid;
  gap: 16px;
}

.flash-filter-bar {
  display: flex;
  justify-content: center;
}

.flashcard {
  position: relative;
  display: grid;
  place-items: center;
  width: 100%;
  min-height: 260px;
  padding: 38px 22px;
  border: 1px solid rgba(0, 127, 122, 0.25);
  border-radius: 8px;
  background:
    linear-gradient(135deg, rgba(231, 246, 242, 1), rgba(250, 238, 242, 0.9)),
    #fff;
  color: var(--ink);
  text-align: center;
  box-shadow: 0 12px 28px rgba(0, 95, 91, 0.08);
  overflow: hidden;
}

.flashcard::after {
  content: attr(data-status-flash);
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  color: rgba(0, 95, 91, 0.34);
  font-size: clamp(7rem, 28vw, 18rem);
  font-weight: 900;
  line-height: 1;
  opacity: 0;
  pointer-events: none;
  transform: scale(0.86);
  transition:
    opacity 160ms ease,
    transform 160ms ease;
}

.flashcard.show-status-flash::after {
  opacity: 1;
  transform: scale(1);
}

.card-meta {
  position: absolute;
  top: 14px;
  right: 14px;
  color: var(--muted);
  font-size: 0.9rem;
  font-weight: 700;
}

.card-front,
.card-back {
  display: block;
  max-width: 780px;
  font-size: clamp(1.55rem, 6vw, 3.7rem);
  font-weight: 850;
  line-height: 1.1;
  overflow-wrap: anywhere;
}

.card-back {
  display: none;
  color: var(--teal-dark);
  font-size: clamp(1.25rem, 5vw, 2.8rem);
}

.flashcard.is-flipped .card-front {
  display: none;
}

.flashcard.is-flipped .card-back {
  display: block;
}

.flash-actions,
.flash-progress {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
  justify-content: center;
}

.flash-progress {
  justify-content: space-between;
  color: var(--muted);
  font-weight: 700;
}

.mark-card-button {
  display: inline-grid;
  place-items: center;
  min-width: 48px;
  padding: 0 12px;
  font-size: 1.45rem;
  line-height: 1;
}

.mark-card-button.learned {
  border-color: rgba(32, 122, 66, 0.55);
  color: var(--success);
}

.mark-card-button.review {
  border-color: rgba(185, 48, 48, 0.45);
  color: var(--danger);
}

.mark-card-button.learned.is-active,
.mark-card-button.learned:hover {
  background: #f0fbf3;
  border-color: var(--success);
}

.mark-card-button.review.is-active,
.mark-card-button.review:hover {
  background: #fff3f3;
  border-color: var(--danger);
}

.mark-card-button:disabled,
.flashcard:disabled,
.secondary-button:disabled,
.primary-button:disabled {
  cursor: not-allowed;
  opacity: 0.55;
}

.reference-table {
  display: grid;
  gap: 8px;
}

.reference-row {
  display: grid;
  grid-template-columns: minmax(150px, 0.8fr) minmax(150px, 0.8fr) minmax(0, 1.2fr);
  gap: 10px;
  align-items: start;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
}

.reference-row strong {
  color: var(--teal-dark);
}

.reference-row em {
  color: var(--muted);
}

.notice-box {
  display: flex;
  gap: 10px;
  align-items: flex-start;
  margin-top: 14px;
  padding: 12px;
  border: 1px solid rgba(215, 151, 31, 0.5);
  border-radius: 8px;
  background: #fff8e8;
}

.notice-box strong {
  color: var(--amber);
}

@media (max-width: 780px) {
  .app-shell {
    width: min(100% - 20px, 1120px);
    padding-top: 10px;
  }

  .topbar,
  .tabs,
  .two-col,
  .flag-grid,
  .category-board,
  .reference-row {
    grid-template-columns: 1fr;
  }

  .topbar {
    padding: 22px;
  }

  .score-panel {
    width: 100%;
    height: auto;
    min-height: 82px;
  }

  .panel-heading {
    align-items: stretch;
    flex-direction: column;
  }

  .exercise-block,
  .reference-section,
  .flashcard-area {
    padding: 16px;
  }

  .answer-row {
    grid-template-columns: 1fr;
  }

  .free-row {
    grid-template-columns: 1fr;
  }

  .flag-example {
    grid-template-columns: max-content minmax(0, 1fr);
  }

  .number-find-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .mashup-row {
    grid-template-columns: 1fr;
  }
}