:root {
  --bg: #f7fbff;
  --surface: #ffffff;
  --surface-strong: #f1f7ff;
  --text: #102033;
  --muted: #66758a;
  --line: #dbe8f7;
  --accent: #2563eb;
  --accent-strong: #1d4ed8;
  --accent-soft: #dbeafe;
  --success: #16a34a;
  --success-soft: #dcfce7;
  --danger: #dc2626;
  --danger-soft: #fee2e2;
  --warning: #f59e0b;
  --shadow: 0 18px 45px rgba(37, 99, 235, 0.12);
  --radius: 8px;
  --ease: 180ms ease;
}

* {
  box-sizing: border-box;
}

html {
  color-scheme: light;
}

html.dark {
  color-scheme: dark;
  --bg: #07111f;
  --surface: #0f1c2d;
  --surface-strong: #132844;
  --text: #eef6ff;
  --muted: #9eb0c8;
  --line: #243853;
  --accent: #60a5fa;
  --accent-strong: #93c5fd;
  --accent-soft: #123763;
  --success: #4ade80;
  --success-soft: #12331f;
  --danger: #f87171;
  --danger-soft: #3a1618;
  --warning: #fbbf24;
  --shadow: 0 18px 45px rgba(0, 0, 0, 0.28);
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    radial-gradient(circle at top left, rgba(37, 99, 235, 0.12), transparent 34rem),
    var(--bg);
  color: var(--text);
  font-family:
    Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
    sans-serif;
}

button,
input,
select,
textarea {
  font: inherit;
}

button {
  cursor: pointer;
}

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

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 28px;
}

.brand-button {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 0;
  border: 0;
  background: transparent;
  color: var(--text);
  text-align: left;
}

.brand-mark {
  display: grid;
  width: 44px;
  height: 44px;
  place-items: center;
  border-radius: var(--radius);
  background: linear-gradient(135deg, var(--accent), #38bdf8);
  color: #ffffff;
  font-weight: 800;
  letter-spacing: 0;
  box-shadow: var(--shadow);
}

.brand-button strong,
.brand-button small {
  display: block;
}

.brand-button small {
  margin-top: 2px;
  color: var(--muted);
}

.topbar-actions {
  display: flex;
  align-items: center;
  gap: 10px;
}

.app-main {
  animation: fadeUp 220ms ease both;
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.1fr) minmax(280px, 0.9fr);
  gap: 24px;
  align-items: stretch;
}

.panel,
.card,
.question-card,
.score-card {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: rgba(255, 255, 255, 0.88);
  box-shadow: var(--shadow);
}

html.dark .panel,
html.dark .card,
html.dark .question-card,
html.dark .score-card {
  background: rgba(15, 28, 45, 0.9);
}

.panel {
  padding: clamp(24px, 4vw, 40px);
}

.headline {
  margin: 0;
  max-width: 760px;
  font-size: clamp(2.15rem, 5vw, 4.5rem);
  line-height: 0.98;
  letter-spacing: 0;
}

.lead {
  max-width: 680px;
  margin: 18px 0 0;
  color: var(--muted);
  font-size: 1.05rem;
  line-height: 1.65;
}

.stat-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  margin-top: 28px;
}

.stat {
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface-strong);
}

.stat strong {
  display: block;
  font-size: 1.65rem;
}

.stat span {
  color: var(--muted);
  font-size: 0.9rem;
}

.auth-card {
  padding: 24px;
}

.auth-tabs,
.mode-row {
  display: flex;
  gap: 8px;
  padding: 6px;
  border-radius: var(--radius);
  background: var(--surface-strong);
}

.tab-button,
.mode-button {
  flex: 1;
  border: 0;
  border-radius: 6px;
  padding: 10px 12px;
  background: transparent;
  color: var(--muted);
  transition: background var(--ease), color var(--ease), transform var(--ease);
}

.tab-button.active,
.mode-button.active {
  background: var(--surface);
  color: var(--accent);
  box-shadow: 0 8px 20px rgba(37, 99, 235, 0.12);
}

.form {
  display: grid;
  gap: 14px;
  margin-top: 18px;
}

.field {
  display: grid;
  gap: 7px;
}

.field label {
  color: var(--muted);
  font-size: 0.92rem;
  font-weight: 700;
}

.field input,
.field select,
.field textarea,
.answer-input {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 13px 14px;
  background: var(--surface);
  color: var(--text);
  outline: none;
  transition: border var(--ease), box-shadow var(--ease), transform var(--ease);
}

.field textarea {
  min-height: 108px;
  resize: vertical;
  line-height: 1.45;
}

.field input[type="file"] {
  padding: 11px;
}

.field input:focus,
.field select:focus,
.field textarea:focus,
.answer-input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 4px rgba(37, 99, 235, 0.14);
}

.primary-button,
.secondary-button,
.ghost-button,
.danger-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  min-height: 42px;
  border-radius: var(--radius);
  border: 1px solid transparent;
  padding: 10px 16px;
  font-weight: 800;
  text-decoration: none;
  transition: transform var(--ease), box-shadow var(--ease), background var(--ease), color var(--ease);
}

.primary-button {
  background: var(--accent);
  color: #ffffff;
  box-shadow: 0 14px 28px rgba(37, 99, 235, 0.24);
}

.primary-button:hover,
.secondary-button:hover,
.ghost-button:hover,
.danger-button:hover,
.category-card:hover {
  transform: translateY(-2px);
}

.primary-button:active,
.secondary-button:active,
.ghost-button:active,
.danger-button:active {
  transform: translateY(0);
}

.secondary-button {
  background: var(--accent-soft);
  color: var(--accent-strong);
  border-color: rgba(37, 99, 235, 0.18);
}

.ghost-button {
  background: var(--surface);
  color: var(--text);
  border-color: var(--line);
}

.danger-button {
  background: var(--danger-soft);
  color: var(--danger);
  border-color: rgba(220, 38, 38, 0.2);
}

.message {
  min-height: 22px;
  color: var(--danger);
  font-weight: 700;
}

.message.ok {
  color: var(--success);
}

.section-head {
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 18px;
}

.section-head h1,
.section-head h2 {
  margin: 0;
}

.section-head p {
  margin: 6px 0 0;
  color: var(--muted);
}

.category-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 14px;
}

.category-card {
  position: relative;
  display: grid;
  gap: 14px;
  min-height: 236px;
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
  text-align: left;
  color: var(--text);
  box-shadow: var(--shadow);
  transition: transform var(--ease), border var(--ease), box-shadow var(--ease);
}

.category-card:hover {
  border-color: rgba(37, 99, 235, 0.45);
}

.category-number {
  display: grid;
  width: 38px;
  height: 38px;
  place-items: center;
  border-radius: var(--radius);
  background: var(--accent-soft);
  color: var(--accent-strong);
  font-weight: 900;
}

.category-card h3 {
  margin: 0;
  font-size: 1.12rem;
}

.category-card p {
  margin: 0;
  color: var(--muted);
  line-height: 1.45;
}

.mini-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: auto;
  color: var(--muted);
  font-size: 0.88rem;
}

.pill {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  border-radius: 999px;
  padding: 6px 10px;
  background: var(--surface-strong);
  color: var(--muted);
  font-size: 0.86rem;
  font-weight: 800;
}

.question-shell {
  display: grid;
  gap: 16px;
}

.practice-top {
  display: grid;
  gap: 10px;
}

.progress-row {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  color: var(--muted);
  font-weight: 800;
}

.progress-track {
  overflow: hidden;
  height: 10px;
  border-radius: 999px;
  background: var(--surface-strong);
}

.progress-fill {
  width: 0%;
  height: 100%;
  border-radius: inherit;
  background: linear-gradient(90deg, var(--accent), #38bdf8);
  transition: width 260ms ease;
}

.question-card {
  padding: clamp(22px, 4vw, 38px);
}

.question-meta {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  color: var(--muted);
  font-weight: 800;
}

.question-text {
  margin: 22px 0;
  font-size: clamp(1.55rem, 3.5vw, 2.6rem);
  line-height: 1.18;
  letter-spacing: 0;
}

.answer-area {
  display: grid;
  gap: 14px;
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.feedback {
  display: none;
  border-radius: var(--radius);
  padding: 16px;
  border: 1px solid var(--line);
  background: var(--surface-strong);
  line-height: 1.55;
}

.feedback.show {
  display: block;
  animation: fadeUp 180ms ease both;
}

.feedback.correct {
  border-color: rgba(22, 163, 74, 0.35);
  background: var(--success-soft);
}

.feedback.incorrect {
  border-color: rgba(220, 38, 38, 0.35);
  background: var(--danger-soft);
}

.feedback strong {
  display: block;
  margin-bottom: 6px;
}

.correct-burst {
  animation: correctPop 520ms ease both;
}

.score-card {
  width: min(720px, 100%);
  margin: 0 auto;
  padding: clamp(24px, 5vw, 44px);
  text-align: center;
}

.score-number {
  margin: 12px 0 0;
  font-size: clamp(3rem, 10vw, 6rem);
  line-height: 1;
  color: var(--accent);
}

.score-card p {
  color: var(--muted);
  line-height: 1.6;
}

.teacher-grid {
  display: grid;
  grid-template-columns: minmax(260px, 0.85fr) minmax(0, 1.15fr);
  gap: 16px;
}

.calendar-layout {
  display: grid;
  grid-template-columns: minmax(320px, 0.92fr) minmax(0, 1.08fr);
  gap: 16px;
  align-items: start;
}

.calendar-panel,
.date-panel {
  padding: 20px;
}

.calendar-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 16px;
}

.calendar-toolbar h2 {
  margin: 0;
  font-size: 1.2rem;
  text-align: center;
}

.calendar-grid {
  display: grid;
  grid-template-columns: repeat(7, minmax(0, 1fr));
  gap: 8px;
}

.calendar-weekday {
  padding: 6px 2px;
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 900;
  text-align: center;
  text-transform: uppercase;
}

.calendar-cell {
  display: grid;
  align-content: start;
  gap: 4px;
  min-height: 82px;
  padding: 10px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--text);
  text-align: left;
  transition: border var(--ease), transform var(--ease), box-shadow var(--ease);
}

.calendar-cell:not(.calendar-empty):hover {
  transform: translateY(-2px);
  border-color: rgba(37, 99, 235, 0.45);
}

.calendar-cell strong {
  font-size: 0.95rem;
}

.calendar-cell span,
.calendar-cell small {
  min-height: 14px;
  color: var(--muted);
  font-size: 0.72rem;
  line-height: 1.2;
}

.calendar-cell.today {
  background: var(--accent-soft);
}

.calendar-cell.selected {
  border-color: var(--accent);
  box-shadow: 0 0 0 4px rgba(37, 99, 235, 0.12);
}

.calendar-empty {
  pointer-events: none;
  background: transparent;
  box-shadow: none;
}

.compact-head {
  margin-bottom: 10px;
}

.assignment-form,
.submission-form,
.feedback-form {
  margin: 14px 0 18px;
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface-strong);
}

.resource-columns {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
  margin-top: 16px;
}

.resource-section {
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
}

.resource-section h3 {
  margin: 0 0 12px;
}

.assignment-stack {
  display: grid;
  gap: 14px;
  margin-top: 16px;
}

.assignment-card,
.submission-card,
.resource-strip {
  display: grid;
  gap: 12px;
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
}

.assignment-head,
.submission-head,
.file-row {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 12px;
}

.assignment-head h3,
.resource-strip h3,
.submission-list h4 {
  margin: 0;
}

.assignment-head p,
.submission-card p {
  margin: 6px 0 0;
  color: var(--muted);
  line-height: 1.5;
  white-space: pre-wrap;
}

.submission-head span,
.file-row span {
  display: block;
  margin-top: 4px;
  color: var(--muted);
  font-size: 0.86rem;
}

.submission-list {
  display: grid;
  gap: 10px;
}

.student-category {
  margin-top: 16px;
}

.file-list {
  display: grid;
  gap: 8px;
}

.file-row {
  align-items: center;
  padding: 10px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface-strong);
}

.file-row strong {
  overflow-wrap: anywhere;
}

.student-list {
  display: grid;
  gap: 10px;
}

.student-row {
  width: 100%;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--text);
  text-align: left;
}

.student-row.active {
  border-color: var(--accent);
  box-shadow: 0 0 0 4px rgba(37, 99, 235, 0.12);
}

.student-row strong,
.student-row span {
  display: block;
}

.student-row span {
  margin-top: 4px;
  color: var(--muted);
}

.table-wrap {
  overflow-x: auto;
}

table {
  width: 100%;
  border-collapse: collapse;
  min-width: 560px;
}

th,
td {
  padding: 12px;
  border-bottom: 1px solid var(--line);
  text-align: left;
}

th {
  color: var(--muted);
  font-size: 0.84rem;
  text-transform: uppercase;
}

.empty {
  padding: 24px;
  border: 1px dashed var(--line);
  border-radius: var(--radius);
  color: var(--muted);
  text-align: center;
}

.hidden {
  display: none !important;
}

.confetti-piece {
  position: fixed;
  top: -12px;
  width: 8px;
  height: 14px;
  border-radius: 3px;
  pointer-events: none;
  animation: confettiFall 900ms linear forwards;
  z-index: 20;
}

@keyframes fadeUp {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes correctPop {
  0% {
    transform: scale(1);
  }
  40% {
    transform: scale(1.02);
    box-shadow: 0 0 0 6px rgba(22, 163, 74, 0.14);
  }
  100% {
    transform: scale(1);
  }
}

@keyframes confettiFall {
  to {
    transform: translate3d(var(--drift), 105vh, 0) rotate(540deg);
    opacity: 0;
  }
}

@media (max-width: 940px) {
  .hero,
  .teacher-grid,
  .calendar-layout,
  .resource-columns {
    grid-template-columns: 1fr;
  }

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

@media (max-width: 640px) {
  .app-shell {
    width: min(100% - 20px, 1120px);
    padding-top: 14px;
  }

  .topbar,
  .section-head,
  .question-meta,
  .progress-row {
    align-items: stretch;
    flex-direction: column;
  }

  .topbar-actions,
  .button-row {
    width: 100%;
  }

  .topbar-actions > *,
  .button-row > * {
    flex: 1;
  }

  .category-grid,
  .stat-grid {
    grid-template-columns: 1fr;
  }

  .category-card {
    min-height: auto;
  }

  .calendar-grid {
    gap: 5px;
  }

  .calendar-cell {
    min-height: 68px;
    padding: 7px;
  }

  .calendar-cell span,
  .calendar-cell small {
    font-size: 0.66rem;
  }

  .assignment-head,
  .submission-head,
  .file-row {
    align-items: stretch;
    flex-direction: column;
  }
}