:root {
  --ink: #26302b;
  --muted: #64706a;
  --paper: #f7fbff;
  --sheet: #ffffff;
  --mint: #dff4df;
  --sky: #dff1ff;
  --peach: #ffdeda;
  --yellow: #ffef9f;
  --green: #2f8f71;
  --blue: #2d6fa3;
  --rose: #d76673;
  --line: #27332d;
  --soft-line: #d6e0db;
  --shadow: 7px 8px 0 rgba(38, 48, 43, 0.12);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  color: var(--ink);
  /* Muon doi nen: thay file assets/page-background.svg bang anh moi cung ten. */
  background:
    url("assets/page-background.svg") top center repeat-y,
    linear-gradient(rgba(45, 111, 163, 0.05) 1px, transparent 1px),
    linear-gradient(90deg, rgba(47, 143, 113, 0.05) 1px, transparent 1px),
    var(--paper);
  background-size: min(1440px, 100vw) auto, 28px 28px, 28px 28px, auto;
  font-family: "Trebuchet MS", Arial, sans-serif;
  letter-spacing: 0;
}

img {
  display: block;
  max-width: 100%;
}

a {
  color: inherit;
  text-decoration: none;
}

button,
input,
select {
  font: inherit;
}

main {
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  gap: 14px;
  min-height: 74px;
  padding: 12px clamp(16px, 4vw, 54px);
  background: rgba(247, 251, 255, 0.92);
  backdrop-filter: blur(12px);
}

.sketch-line {
  border-bottom: 3px solid var(--line);
  box-shadow: 0 4px 0 rgba(38, 48, 43, 0.08);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  min-width: max-content;
  font-weight: 900;
}

.brand-badge {
  display: grid;
  width: 42px;
  height: 42px;
  place-items: center;
  color: #fff;
  background: var(--green);
  border: 3px solid var(--line);
  border-radius: 8px 7px 8px 6px;
  box-shadow: 3px 3px 0 var(--yellow);
}

.main-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-left: auto;
  font-weight: 800;
}

.main-nav a,
.user-pill {
  padding: 9px 12px;
  background: #fff;
  border: 2px solid var(--line);
  border-radius: 8px 7px 6px 8px;
}

.user-pill {
  background: var(--yellow);
  font-weight: 900;
}

.button {
  display: inline-flex;
  min-height: 44px;
  align-items: center;
  justify-content: center;
  padding: 10px 16px;
  border: 3px solid var(--line);
  border-radius: 8px;
  cursor: pointer;
  font-weight: 900;
  box-shadow: 4px 4px 0 rgba(38, 48, 43, 0.18);
}

.button:hover {
  transform: translate(1px, 1px);
  box-shadow: 3px 3px 0 rgba(38, 48, 43, 0.2);
}

.primary {
  color: #fff;
  background: var(--green);
}

.secondary {
  background: var(--yellow);
}

.danger {
  color: #fff;
  background: var(--rose);
}

.ghost {
  background: #fff;
}

.sketch-card {
  background: var(--sheet);
  border: 3px solid var(--line);
  border-radius: 8px 7px 8px 6px;
  box-shadow: var(--shadow);
}

.eyebrow {
  margin: 0 0 9px;
  color: var(--blue);
  font-size: 0.84rem;
  font-weight: 900;
  text-transform: uppercase;
}

h1,
h2,
h3,
p {
  overflow-wrap: anywhere;
}

h1 {
  margin: 0;
  font-size: clamp(2.2rem, 6vw, 4.8rem);
  line-height: 1;
}

h2 {
  margin: 0;
  font-size: clamp(1.5rem, 3vw, 2.5rem);
  line-height: 1.1;
}

p {
  color: var(--muted);
  line-height: 1.7;
}

.home-hero,
.auth-shell {
  display: grid;
  grid-template-columns: minmax(0, 1.05fr) minmax(300px, 0.8fr);
  gap: clamp(24px, 6vw, 70px);
  align-items: center;
  min-height: calc(100vh - 74px);
  padding: clamp(32px, 6vw, 80px) 0;
}

.hero-text {
  display: grid;
  gap: 16px;
}

.hero-text p {
  max-width: 700px;
  font-size: 1.08rem;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.hero-mascot,
.auth-mascot {
  width: min(420px, 100%);
  justify-self: center;
}

.quick-stats,
.feature-grid,
.grade-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 18px;
  margin: 28px 0;
}

.stat,
.feature,
.grade-card {
  padding: 22px;
}

.stat strong,
.grade-card strong {
  display: block;
  color: var(--green);
  font-size: clamp(2.5rem, 6vw, 5rem);
  line-height: 1;
}

.stat span,
.grade-card p {
  color: var(--muted);
  font-weight: 800;
}

.feature {
  display: grid;
  gap: 12px;
  min-height: 310px;
}

.feature img {
  width: 150px;
  height: 130px;
  object-fit: contain;
}

.page-heading {
  padding: clamp(34px, 6vw, 80px) 0 20px;
  max-width: 900px;
}

.auth-hero,
.auth-form,
.tips-layout,
.test-form,
.exam-result,
.lesson-reader {
  padding: clamp(20px, 4vw, 36px);
}

.auth-forms {
  display: grid;
  gap: 18px;
}

.auth-form {
  display: grid;
  gap: 14px;
}

label {
  display: grid;
  gap: 7px;
  color: var(--ink);
  font-weight: 900;
}

.check-row {
  display: flex;
  align-items: center;
  gap: 10px;
}

.check-row input {
  width: auto;
  min-height: auto;
}

input,
select,
textarea {
  width: 100%;
  min-height: 44px;
  padding: 10px 12px;
  color: var(--ink);
  background: #fff;
  border: 2px solid var(--line);
  border-radius: 8px;
}

textarea {
  min-height: 120px;
  resize: vertical;
  line-height: 1.6;
}

input:focus,
select:focus,
textarea:focus {
  outline: 4px solid rgba(255, 239, 159, 0.75);
}

.alert,
.install-hint {
  padding: 14px 16px;
  background: var(--peach);
  border: 3px solid var(--line);
  border-radius: 8px;
  font-weight: 800;
}

.alert p {
  margin: 0;
  color: var(--ink);
}

.tips-layout {
  display: grid;
  grid-template-columns: minmax(220px, 0.75fr) minmax(0, 1.4fr);
  gap: 22px;
  margin-bottom: 50px;
}

.tips-list {
  display: grid;
  align-content: start;
  gap: 10px;
}

.tip-item {
  min-height: 52px;
  padding: 12px;
  text-align: left;
  background: #fff;
  border: 2px solid var(--line);
  border-radius: 8px;
  cursor: pointer;
  font-weight: 900;
}

.tip-item.active,
.tip-item:hover {
  background: var(--yellow);
}

.tip-preview {
  display: grid;
  grid-template-columns: minmax(160px, 260px) minmax(0, 1fr);
  gap: 20px;
  align-items: center;
}

.tip-preview img {
  width: 100%;
  min-height: 220px;
  object-fit: contain;
  background: var(--sky);
  border: 2px dashed var(--line);
  border-radius: 8px;
}

.sub-nav {
  margin: 0 0 20px;
}

.chapter-list {
  display: grid;
  gap: 18px;
  margin-bottom: 50px;
}

.chapter-block {
  display: grid;
  gap: 14px;
  padding: 20px;
}

.folder-note {
  margin: 8px 0 0;
  color: var(--blue);
  font-family: Consolas, "Courier New", monospace;
  font-weight: 800;
}

.lesson-list {
  display: grid;
  gap: 10px;
  padding: 0;
  margin: 0;
  list-style: none;
}

.lesson-list li {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
  padding: 12px;
  background: var(--mint);
  border: 2px solid var(--line);
  border-radius: 8px;
}

.lesson-list a {
  font-weight: 900;
}

.empty-note {
  margin: 0;
  color: var(--muted);
  font-weight: 800;
}

.lesson-content {
  margin-top: 22px;
  padding: 20px;
  background: linear-gradient(#fff 31px, rgba(47, 143, 113, 0.12) 32px);
  background-size: 100% 32px;
  border: 2px solid var(--soft-line);
  border-radius: 8px;
  line-height: 2;
}

.image-gallery {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
  margin-top: 22px;
}

.image-gallery img {
  width: 100%;
  max-height: 420px;
  object-fit: contain;
  background: #fff;
  border: 3px solid var(--line);
  border-radius: 8px;
}

.form-row {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 16px;
}

.test-form {
  display: grid;
  gap: 18px;
  margin-bottom: 28px;
}

.progress-form,
.attempt-form {
  display: grid;
  gap: 16px;
  margin-top: 22px;
}

.form-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.answer-options {
  display: grid;
  gap: 8px;
  margin: 12px 0;
}

.answer-options label {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 10px;
  background: var(--mint);
  border: 2px solid var(--line);
  border-radius: 8px;
}

.answer-options input {
  width: auto;
  min-height: auto;
  margin-top: 4px;
}

.score-card,
.progress-panel {
  padding: 20px;
  margin-bottom: 22px;
}

.ai-grader-panel {
  display: grid;
  gap: 12px;
  padding: 20px;
  margin-bottom: 22px;
  background: var(--mint);
}

.ai-grader-panel form {
  margin: 0;
}

.ai-feedback {
  display: grid;
  gap: 6px;
  margin-top: 12px;
  padding: 12px;
  background: var(--mint);
  border: 2px solid var(--line);
  border-radius: 8px;
}

.ai-feedback p {
  margin: 0;
  line-height: 1.6;
}

.muted-feedback {
  background: var(--sky);
}

.progress-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 20px;
  margin-bottom: 54px;
}

.progress-list {
  display: grid;
  gap: 10px;
  padding: 0;
  list-style: none;
}

.progress-list li {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 12px;
  background: var(--sky);
  border: 2px solid var(--line);
  border-radius: 8px;
}

.progress-list a,
.progress-list strong {
  font-weight: 900;
}

.progress-main {
  display: grid;
  gap: 4px;
  min-width: 0;
}

.progress-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: flex-end;
  gap: 8px;
}

.progress-actions form {
  margin: 0;
}

.small-button {
  min-height: 36px;
  padding: 7px 12px;
}

.chapter-picker {
  display: grid;
  gap: 10px;
}

.chapter-set {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
}

.chapter-check {
  display: flex;
  align-items: flex-start;
  gap: 9px;
  padding: 12px;
  background: var(--sky);
  border: 2px solid var(--line);
  border-radius: 8px;
}

.chapter-check input {
  width: auto;
  min-height: auto;
  margin-top: 4px;
}

.exam-result {
  margin-bottom: 54px;
}

.admin-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  padding: 12px;
  margin: 0 0 22px;
}

.admin-tabs a {
  padding: 10px 12px;
  background: #fff;
  border: 2px solid var(--line);
  border-radius: 8px;
  font-weight: 900;
}

.admin-tabs a.active {
  background: var(--yellow);
}

.admin-panel {
  padding: 20px;
  margin-bottom: 22px;
}

.admin-panel-heading {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.admin-action-grid,
.admin-toolbar,
.admin-edit-form {
  display: grid;
  gap: 14px;
}

.admin-action-grid {
  grid-template-columns: repeat(auto-fit, minmax(170px, 1fr));
}

.admin-toolbar {
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  align-items: end;
}

.admin-mini-filter {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.admin-mini-filter select {
  width: auto;
}

.admin-summary {
  display: grid;
  gap: 6px;
  margin-bottom: 16px;
}

.admin-summary p,
.admin-answer-box p {
  margin: 0;
}

.admin-answer-box {
  display: grid;
  gap: 6px;
  margin-top: 12px;
  padding: 12px;
  background: var(--mint);
  border: 2px solid var(--line);
  border-radius: 8px;
}

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

.admin-table {
  width: 100%;
  min-width: 900px;
  border-collapse: collapse;
  background: #fff;
}

.admin-table th,
.admin-table td {
  padding: 10px;
  border: 2px solid var(--line);
  text-align: left;
  vertical-align: top;
}

.admin-table th {
  background: var(--yellow);
}

.admin-pagination {
  display: flex;
  flex-wrap: wrap;
  align-items: end;
  justify-content: space-between;
  gap: 12px;
  margin-top: 16px;
}

.admin-page-links,
.admin-page-jump {
  display: flex;
  flex-wrap: wrap;
  align-items: end;
  gap: 8px;
}

.admin-page-jump label {
  min-width: 130px;
}

.admin-image-field {
  display: grid;
  gap: 12px;
  padding: 12px;
  background: var(--sky);
  border: 2px dashed var(--line);
  border-radius: 8px;
}

.admin-tip-box {
  display: grid;
  gap: 12px;
  padding: 14px;
  background: var(--mint);
  border: 2px dashed var(--line);
  border-radius: 8px;
}

.admin-image-field img,
.question-image {
  width: min(100%, 460px);
  max-height: 320px;
  object-fit: contain;
  background: #fff;
  border: 2px solid var(--line);
  border-radius: 8px;
}

.question-image {
  margin: 10px 0;
}

.inline-check {
  display: flex;
  align-items: center;
  gap: 8px;
}

.inline-check input {
  width: auto;
  min-height: auto;
}

.admin-card-list {
  display: grid;
  gap: 12px;
  padding: 0;
  list-style: none;
}

.admin-card-list li {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 110px auto;
  gap: 12px;
  align-items: center;
  padding: 12px;
  background: var(--sky);
  border: 2px solid var(--line);
  border-radius: 8px;
}

.admin-card-list div {
  display: grid;
  gap: 4px;
}

.admin-card-list strong {
  font-size: 1.05rem;
}

.admin-card-list span {
  color: var(--muted);
  font-weight: 800;
}

.admin-card-list img {
  width: 100%;
  height: 76px;
  object-fit: contain;
  background: #fff;
  border: 2px solid var(--line);
  border-radius: 8px;
}

.lesson-tip-panel {
  display: grid;
  gap: 16px;
  padding: clamp(18px, 4vw, 30px);
  margin: 22px 0 30px;
  background: rgba(223, 244, 223, 0.92);
  border: 3px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.lesson-tip-heading {
  max-width: 760px;
}

.lesson-tip-heading h2,
.lesson-tip-heading p {
  margin-top: 0;
}

.lesson-tip-list {
  display: grid;
  gap: 12px;
  padding: 0;
  list-style: none;
}

.lesson-tip-list li {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 12px;
  align-items: center;
  padding: 14px;
  background: #fff;
  border: 2px dashed var(--line);
  border-radius: 8px;
}

.lesson-tip-list strong {
  font-size: 1.05rem;
}

.lesson-tip-list p {
  margin: 6px 0;
  line-height: 1.6;
}

.lesson-tip-list span {
  color: var(--muted);
  font-weight: 900;
}

.exam-meta {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  margin: 16px 0;
}

.exam-meta p,
.question-list li {
  padding: 14px;
  background: #fff;
  border: 2px dashed var(--line);
  border-radius: 8px;
}

.question-list {
  display: grid;
  gap: 12px;
  padding-left: 26px;
}

.difficulty {
  display: inline-flex;
  margin: 4px 0 10px;
  padding: 5px 9px;
  background: var(--yellow);
  border: 2px solid var(--line);
  border-radius: 8px;
  font-weight: 900;
}

.options {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 8px;
  margin: 10px 0;
}

details {
  margin-top: 10px;
}

summary {
  cursor: pointer;
  font-weight: 900;
}

.site-footer {
  margin-top: 40px;
  padding: 26px clamp(16px, 4vw, 54px);
  background: var(--ink);
}

.site-footer p {
  width: min(1180px, 100%);
  margin: 0 auto;
  color: #fff;
}

@media (max-width: 900px) {
  .home-hero,
  .auth-shell,
  .tips-layout,
  .tip-preview {
    grid-template-columns: 1fr;
  }

  .quick-stats,
  .feature-grid,
  .grade-grid,
  .exam-meta,
  .admin-action-grid,
  .admin-toolbar,
  .progress-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 680px) {
  main {
    width: min(100% - 20px, 1180px);
  }

  .site-header {
    align-items: flex-start;
    flex-direction: column;
  }

  .main-nav {
    margin-left: 0;
  }

  .form-row,
  .chapter-set,
  .options,
  .image-gallery {
    grid-template-columns: 1fr;
  }

  .progress-list li {
    align-items: flex-start;
    flex-direction: column;
  }

  .lesson-tip-list li {
    grid-template-columns: 1fr;
  }

  .progress-actions {
    justify-content: flex-start;
  }

  .admin-card-list li {
    grid-template-columns: 1fr;
  }

  .admin-card-list img {
    width: min(100%, 180px);
  }
}