/* ===== Reset & Base ===== */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --color-bg: #f7f8fa;
  --color-surface: #ffffff;
  --color-primary: #1865f2;
  --color-primary-light: #e8f0fe;
  --color-text: #21242c;
  --color-text-secondary: #6b7280;
  --color-border: #e4e6ea;
  --color-correct: #0d904f;
  --color-correct-bg: #e6f4ed;
  --color-incorrect: #d92916;
  --color-incorrect-bg: #fde8e6;
  --radius: 8px;
  --shadow: 0 1px 3px rgba(0,0,0,0.08);
  --max-width: 800px;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Noto Sans KR', sans-serif;
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.7;
  font-size: 16px;
}

a {
  color: var(--color-primary);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

/* ===== Header ===== */
header {
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 0;
  z-index: 100;
}

.header-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 12px 20px;
  display: flex;
  align-items: center;
  gap: 16px;
}

.logo a {
  color: var(--color-text);
  font-size: 20px;
  font-weight: 700;
}

.logo a:hover {
  text-decoration: none;
}

.breadcrumb {
  font-size: 14px;
  color: var(--color-text-secondary);
}

.breadcrumb a {
  color: var(--color-text-secondary);
}

.breadcrumb span {
  margin: 0 6px;
}

/* ===== Home: Course Grid ===== */
.home {
  max-width: 960px;
  margin: 0 auto;
  padding: 32px 20px;
}

.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
}

.unit-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 24px;
  cursor: pointer;
  transition: box-shadow 0.2s, border-color 0.2s;
}

.unit-card:hover {
  border-color: var(--color-primary);
  box-shadow: 0 4px 12px rgba(24, 101, 242, 0.1);
}

.unit-card .unit-number {
  font-size: 13px;
  color: var(--color-text-secondary);
  margin-bottom: 4px;
}

.unit-card .unit-title {
  font-size: 18px;
  font-weight: 600;
  margin-bottom: 8px;
}

.unit-card .unit-desc {
  font-size: 14px;
  color: var(--color-text-secondary);
}

/* Color accents for each domain */
.unit-card[data-domain="about"] { border-left: 4px solid #6b7280; }
.unit-card[data-domain="algebra"] { border-left: 4px solid #1865f2; }
.unit-card[data-domain="psda"] { border-left: 4px solid #14bf96; }
.unit-card[data-domain="advanced-math"] { border-left: 4px solid #9059ff; }
.unit-card[data-domain="geometry"] { border-left: 4px solid #ff6b35; }

/* ===== Unit Page ===== */
.unit-page {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 32px 20px;
}

.unit-header {
  margin-bottom: 24px;
}

.unit-header h2 {
  font-size: 28px;
  font-weight: 700;
  margin-bottom: 8px;
}

.unit-header p {
  color: var(--color-text-secondary);
}

.skill-list {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.skill-item {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  transition: border-color 0.2s;
}

.skill-item:hover {
  border-color: var(--color-primary);
}

.skill-item a {
  display: flex;
  align-items: center;
  padding: 16px 20px;
  color: var(--color-text);
  gap: 12px;
}

.skill-item a:hover {
  text-decoration: none;
}

.skill-icon {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  flex-shrink: 0;
}

.skill-icon.lesson { background: var(--color-primary-light); color: var(--color-primary); }
.skill-icon.article { background: #f0f0f0; color: #6b7280; }
.skill-icon.practice { background: #f0e6ff; color: #9059ff; }

/* Skill group (items-based skills) */
.skill-group {
  margin-top: 24px;
  margin-bottom: 8px;
}

.skill-group:first-child {
  margin-top: 0;
}

.skill-group-header {
  margin-bottom: 8px;
}

.skill-group-header h3 {
  font-size: 18px;
  font-weight: 600;
  color: var(--color-text);
}

.skill-group .skill-item {
  margin-bottom: 4px;
}

.skill-icon.example {
  background: #fff3e0;
  color: #e65100;
}

/* Quiz and Test cards */
.quiz-card,
.test-card {
  border-radius: var(--radius);
  padding: 16px 20px;
  font-size: 16px;
  font-weight: 600;
  margin-top: 24px;
  margin-bottom: 8px;
  text-align: center;
}

.quiz-card {
  background: #f0e6ff;
  border: 1px solid #d4b8ff;
  color: #6b21a8;
}

.test-card {
  background: #e0f2fe;
  border: 1px solid #93c5fd;
  color: #1e40af;
}

.sub-unit-header {
  margin-top: 24px;
  margin-bottom: 8px;
}

.sub-unit-header h3 {
  font-size: 18px;
  font-weight: 600;
  color: var(--color-text);
}

.sub-unit-header:first-child {
  margin-top: 0;
}

.skill-name {
  font-size: 16px;
  font-weight: 500;
}

.skill-type {
  font-size: 13px;
  color: var(--color-text-secondary);
}

/* ===== Lesson Page ===== */
.lesson-page {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 32px 20px 80px;
}

.lesson-content h2 {
  font-size: 28px;
  font-weight: 700;
  margin-bottom: 24px;
}

.lesson-content h3 {
  font-size: 20px;
  font-weight: 600;
  margin-top: 32px;
  margin-bottom: 12px;
  color: var(--color-text);
}

.lesson-content p {
  margin-bottom: 16px;
}

.lesson-content ul, .lesson-content ol {
  margin-bottom: 16px;
  padding-left: 24px;
}

.lesson-content li {
  margin-bottom: 8px;
}

/* Data table */
.data-table {
  border-collapse: collapse;
  margin: 12px 0;
  font-size: 15px;
}

.data-table th, .data-table td {
  border: 1px solid var(--color-border);
  padding: 8px 16px;
  text-align: center;
}

.data-table th {
  background: var(--color-bg);
  font-weight: 600;
}

/* Example card wrapper */
.example-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-left: 4px solid var(--color-primary);
  border-radius: var(--radius);
  padding: 20px;
  margin: 20px 0;
}

.example-card-label {
  font-size: 13px;
  font-weight: 700;
  color: var(--color-primary);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 12px;
}

.example-card-question {
  margin-bottom: 12px;
  font-size: 16px;
  line-height: 1.7;
}

/* Collapsible example */
.example-toggle {
  background: var(--color-primary-light);
  border: none;
  border-radius: var(--radius);
  padding: 12px 20px;
  font-size: 15px;
  font-weight: 500;
  color: var(--color-primary);
  cursor: pointer;
  width: 100%;
  text-align: left;
  margin-top: 0;
  margin-bottom: 8px;
  transition: background 0.2s;
}

.example-toggle:hover {
  background: #d4e4fd;
}

.example-toggle::before {
  content: '▶ ';
  font-size: 12px;
}

.example-toggle.open::before {
  content: '▼ ';
}

.example-body {
  display: none;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 20px;
  margin-bottom: 28px;
}

.example-body.open {
  display: block;
}

.example-body .katex-display {
  text-align: left !important;
  margin-left: 1em !important;
}

.example-body .katex-display > .katex {
  text-align: left !important;
}

.explanation .katex-display {
  text-align: left !important;
  margin-left: 1em !important;
}

.explanation .katex-display > .katex {
  text-align: left !important;
}

/* Tip / Note box */
.note-box {
  background: #fffce6;
  border-left: 4px solid #f5c542;
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 16px 20px;
  margin-bottom: 16px;
  font-size: 15px;
}

/* ===== Practice Problems ===== */
.practice-section {
  margin-top: 48px;
}

.practice-section h3 {
  font-size: 22px;
  font-weight: 700;
  margin-bottom: 20px;
  padding-top: 24px;
  border-top: 2px solid var(--color-border);
}

.problem-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 16px;
}

.problem-number {
  font-size: 13px;
  font-weight: 600;
  color: var(--color-text-secondary);
  margin-bottom: 12px;
}

.problem-question {
  font-size: 16px;
  margin-bottom: 16px;
  line-height: 1.8;
}

/* Multiple choice */
.choices {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin-bottom: 16px;
}

.choice-btn {
  background: var(--color-surface);
  border: 2px solid var(--color-border);
  border-radius: var(--radius);
  padding: 12px 16px;
  font-size: 15px;
  cursor: pointer;
  text-align: left;
  transition: border-color 0.2s, background 0.2s;
  font-family: inherit;
  line-height: 1.6;
}

.choice-btn:hover {
  border-color: var(--color-primary);
  background: var(--color-primary-light);
}

.choice-btn.selected {
  border-color: var(--color-primary);
  background: var(--color-primary-light);
}

.choice-btn.correct {
  border-color: var(--color-correct);
  background: var(--color-correct-bg);
}

.choice-btn.incorrect {
  border-color: var(--color-incorrect);
  background: var(--color-incorrect-bg);
}

/* Free response */
.free-response {
  display: flex;
  gap: 12px;
  align-items: center;
  margin-bottom: 16px;
}

.free-response input {
  border: 2px solid var(--color-border);
  border-radius: var(--radius);
  padding: 10px 16px;
  font-size: 16px;
  font-family: inherit;
  width: 200px;
  outline: none;
  transition: border-color 0.2s;
}

.free-response input:focus {
  border-color: var(--color-primary);
}

.free-response input.correct {
  border-color: var(--color-correct);
  background: var(--color-correct-bg);
}

.free-response input.incorrect {
  border-color: var(--color-incorrect);
  background: var(--color-incorrect-bg);
}

/* Dropdown exercise */
.dropdown-exercise {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 16px;
}

.dd-step {
  margin-bottom: 12px;
}

.dd-step p {
  line-height: 2.2;
}

.dd-wrap {
  position: relative;
  display: inline-block;
  vertical-align: middle;
}

.dd-btn {
  border: 2px solid var(--color-border);
  border-radius: 4px;
  padding: 4px 8px;
  font-size: 14px;
  font-family: inherit;
  cursor: pointer;
  background: var(--color-surface);
  transition: border-color 0.2s;
  display: inline-flex;
  align-items: center;
  gap: 6px;
}

.dd-btn:focus {
  border-color: var(--color-primary);
  outline: none;
}

.dd-caret {
  font-size: 11px;
  color: #888;
}

.dd-menu {
  display: none;
  position: absolute;
  top: calc(100% + 2px);
  left: 0;
  min-width: 100%;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 6px;
  box-shadow: 0 4px 14px rgba(0, 0, 0, 0.12);
  z-index: 50;
  padding: 4px;
  white-space: nowrap;
}

.dd-menu.open {
  display: block;
}

.dd-opt {
  display: block;
  width: 100%;
  text-align: left;
  border: none;
  background: none;
  font-size: 14px;
  font-family: inherit;
  padding: 6px 10px;
  border-radius: 4px;
  cursor: pointer;
}

.dd-opt:hover {
  background: #f0f4ff;
}

.dd-wrap.dd-disabled .dd-btn {
  cursor: default;
  opacity: 0.85;
}

.dd-wrap.dd-correct .dd-btn {
  border-color: var(--color-correct);
  background: var(--color-correct-bg);
}

.dd-wrap.dd-incorrect .dd-btn {
  border-color: var(--color-incorrect);
  background: var(--color-incorrect-bg);
}

.lesson-figure {
  margin: 20px auto;
  text-align: center;
}

.lesson-figure img {
  max-width: 420px;
  width: 100%;
  height: auto;
}

.lesson-figure figcaption {
  font-size: 13px;
  color: #666;
  margin-top: 6px;
}

.choice-btn img,
.example-body img,
.problem-question img,
.dd-feedback img,
.note-box img {
  max-width: 300px;
  width: 100%;
  height: auto;
  display: block;
  margin: 6px auto;
}

.graphie-wrap {
  position: relative;
  display: block;
  width: fit-content;
  margin: 8px auto;
  line-height: 0;
}

.graphie-wrap img {
  display: block;
}

.graphie-label {
  position: absolute;
  font-size: 14px;
  line-height: 1;
  white-space: nowrap;
  pointer-events: none;
}

.graphie-label.align-center { transform: translate(-50%, -50%); }
.graphie-label.align-above { transform: translate(-50%, calc(-100% - 4px)); }
.graphie-label.align-below { transform: translate(-50%, 4px); }
.graphie-label.align-left { transform: translate(calc(-100% - 5px), -50%); }
.graphie-label.align-right { transform: translate(5px, -50%); }
.graphie-label.align-above-left { transform: translate(calc(-100% - 3px), calc(-100% - 3px)); }
.graphie-label.align-above-right { transform: translate(3px, calc(-100% - 3px)); }
.graphie-label.align-below-left { transform: translate(calc(-100% - 3px), 3px); }
.graphie-label.align-below-right { transform: translate(3px, 3px); }

.fig-desc {
  display: block;
  font-size: 13px;
  line-height: 1.7;
  color: #555;
  background: #f8f9fb;
  border-left: 3px solid #d0d8e8;
  border-radius: 4px;
  padding: 8px 12px;
  margin: 8px auto 12px;
  max-width: 480px;
  text-align: left;
}

.stem-figure {
  text-align: center;
  margin: 12px auto;
}

.stem-figure svg {
  max-width: 360px;
  width: 100%;
  height: auto;
}

.dd-feedback {
  display: none;
  margin-top: 8px;
  padding: 12px 16px;
  background: #f0f4ff;
  border-radius: var(--radius);
  font-size: 14px;
  line-height: 1.8;
}

.dd-feedback.open {
  display: block;
}

.dd-result {
  margin-top: 12px;
  padding: 12px 16px;
  border-radius: var(--radius);
  font-size: 15px;
  display: none;
}

.dd-result.correct {
  display: block;
  background: var(--color-correct-bg);
  color: var(--color-correct);
}

.dd-result.incorrect {
  display: block;
  background: var(--color-incorrect-bg);
  color: var(--color-incorrect);
}

.dropdown-exercise .btn-check {
  margin-top: 12px;
}

/* Print skill header (section label) */
.print-skill-header {
  display: none;
}

.dd-choices-print { display: none; }
.dd-choice-item {
  display: inline-block;
  margin: 2px 8px 2px 0;
  padding: 2px 8px;
  background: #f0f4ff;
  border: 1px solid #d0d8e8;
  border-radius: 4px;
  font-size: 14px;
}
.dd-answer-section { display: none; }
.print-answer-booklet { display: none; }

/* Print all button */
.btn-print-all {
  display: block;
  margin: 24px auto;
  padding: 12px 32px;
  font-size: 16px;
  font-weight: 600;
  color: var(--color-primary);
  background: var(--color-primary-light);
  border: 2px solid var(--color-primary);
  border-radius: var(--radius);
  cursor: pointer;
  font-family: inherit;
}
.btn-print-all:hover { background: #d4e4fd; }

/* Print-all container: hidden on screen */
#print-all-container { display: none; }
#print-all-container .print-lesson { margin-bottom: 0; }
#print-all-container .print-lesson h2 { font-size: 20px; color: var(--color-primary); border-bottom: 2px solid var(--color-primary); padding-bottom: 6px; margin-bottom: 16px; }
#print-all-container .print-lesson h3 { font-size: 16px; margin-top: 14px; margin-bottom: 8px; }
#print-all-container .print-lesson p { margin-bottom: 8px; }
#print-all-container .print-lesson .note-box { background: #fffce6; border-left: 4px solid #f5c542; padding: 10px 14px; margin: 10px 0; font-size: 14px; }
#print-all-container .print-lesson .example-card { border: 1px solid #e0e0e0; border-left: 4px solid var(--color-primary); border-radius: 6px; padding: 14px 18px; margin: 14px 0; background: #fafbff; }
#print-all-container .print-lesson .example-card-label { font-size: 12px; font-weight: 700; color: var(--color-primary); margin-bottom: 8px; }
#print-all-container .print-lesson .solution-section { display: none; }
#print-all-container .print-lesson .example-body { display: none; }
#print-all-container .print-answer-booklet .answer-content .example-body { display: block; }
#print-all-container .print-answer-booklet .answer-content .solution-section { display: block; }
#print-all-container .data-table { border-collapse: collapse; margin: 8px 0; font-size: 14px; }
#print-all-container .data-table th, #print-all-container .data-table td { border: 1px solid #ddd; padding: 5px 10px; text-align: center; }
#print-all-container .data-table th { background: #f5f5f5; }

/* Check / Explain buttons */
.problem-actions {
  display: flex;
  gap: 8px;
  align-items: center;
  flex-wrap: wrap;
}

.btn {
  border: none;
  border-radius: var(--radius);
  padding: 10px 20px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  font-family: inherit;
  transition: opacity 0.2s;
}

.btn:hover {
  opacity: 0.85;
}

.btn-check {
  background: var(--color-primary);
  color: white;
}

.btn-explain {
  background: transparent;
  color: var(--color-primary);
  border: 1px solid var(--color-primary);
}

.btn-next {
  background: var(--color-primary);
  color: white;
}

/* Feedback */
.feedback {
  margin-top: 12px;
  padding: 12px 16px;
  border-radius: var(--radius);
  font-size: 15px;
  display: none;
}

.feedback.correct {
  display: block;
  background: var(--color-correct-bg);
  color: var(--color-correct);
}

.feedback.incorrect {
  display: block;
  background: var(--color-incorrect-bg);
  color: var(--color-incorrect);
}

/* Explanation */
.explanation {
  display: none;
  margin-top: 12px;
  padding: 16px;
  background: #f0f4ff;
  border-radius: var(--radius);
  font-size: 15px;
  line-height: 1.8;
}

.explanation.open {
  display: block;
}

.explanation p {
  margin-bottom: 12px;
}

.explanation .katex-display {
  margin: 16px 0;
  text-align: left !important;
  margin-left: 1em !important;
}

.explanation .katex-display > .katex {
  text-align: left !important;
}

/* ===== Responsive ===== */
@media (max-width: 600px) {
  .header-inner {
    flex-direction: column;
    align-items: flex-start;
    gap: 4px;
  }

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

  .lesson-content h2 {
    font-size: 22px;
  }

  .problem-card {
    padding: 16px;
  }

  .free-response input {
    width: 100%;
  }

  .free-response {
    flex-direction: column;
    align-items: stretch;
  }
}

/* ===== Print ===== */
@page {
  size: A4;
  margin: 20mm;
}

@media print {
  body { background: #fff; }
  header { display: none; }
  .breadcrumb { display: none; }

  .lesson-content, .practice-section {
    max-width: 100%;
    padding: 0;
  }

  h2, h3 { page-break-after: avoid; }
  .example-card, .example-body, .note-box, .problem-card,
  .katex-display, .dropdown-exercise, table, ul, ol, .lesson-figure {
    page-break-inside: avoid;
  }
  p { orphans: 3; widows: 3; }

  /* Hide solutions in main content */
  .example-body { display: none !important; }
  .example-toggle { display: none; }
  .explanation { display: none !important; }
  .btn-explain { display: none; }

  /* Dropdown: show choices, hide interactive elements */
  .dd-wrap { display: none; }
  .dd-choices-print { display: inline; }
  .dd-feedback { display: none !important; }
  .dd-result, .dropdown-exercise .btn-check { display: none; }
  .dd-answer-section { display: none !important; }

  /* Print skill header */
  .print-skill-header {
    display: block !important;
    font-size: 12px;
    font-weight: 600;
    color: #888;
    border-bottom: 1px solid #ddd;
    padding-bottom: 4px;
    margin-bottom: 12px;
    letter-spacing: 0.3px;
  }

  /* Show print-all container when it's been activated */
  #print-all-container[style*="display: block"] { display: block !important; }

  /* Hide solutions and check buttons */
  .solution-section { display: none !important; }
  .print-answer-booklet .solution-section { display: block !important; }
  .print-answer-booklet .example-body { display: block !important; }
  .btn-check { display: none; }

  /* Answer booklet at the end */
  .print-answer-booklet { display: block !important; page-break-before: always; }
  .print-answer-booklet h2 { font-size: 20px; border-bottom: 2px solid #333; padding-bottom: 8px; margin-bottom: 16px; }
  .print-answer-booklet h3 { font-size: 16px; margin-top: 20px; margin-bottom: 8px; color: #1865f2; }
  .print-answer-skill-group { page-break-before: always; }
  .print-answer-skill-title { font-size: 18px; color: #333; border-bottom: 2px solid #333; padding-bottom: 6px; margin-bottom: 16px; }
  .print-answer-lesson-title { font-size: 14px; color: #1865f2; margin-top: 20px; margin-bottom: 8px; padding-bottom: 4px; border-bottom: 1px dashed #ccc; }
  .print-answer-item { margin: 12px 0; padding: 14px 18px; background: #f8f9fa; border-left: 3px solid #1865f2; border-radius: 4px; page-break-inside: avoid; }
  .print-answer-item .answer-label { font-weight: 700; margin-bottom: 6px; color: #1865f2; font-size: 13px; }
  .print-answer-item .answer-content { font-size: 14px; line-height: 1.8; }
  .print-answer-item .answer-content p { margin-bottom: 6px; }
  .print-answer-item .answer-content ul { padding-left: 20px; margin: 6px 0; }
  .print-answer-item .answer-content li { margin-bottom: 4px; }
  .print-answer-item .answer-content .note-box { margin: 8px 0; font-size: 13px; }
  .print-answer-item .answer-content .data-table { margin: 8px 0; font-size: 13px; }
  .print-answer-item .answer-content .katex-display { text-align: left !important; margin-left: 1em !important; }

  .note-box, .example-card, .example-body, .problem-card {
    -webkit-print-color-adjust: exact;
    print-color-adjust: exact;
  }
}

/* ===== Desmos graphing calculator (global floating panel) ===== */
:root { --desmos-w: 44vw; }
body { box-sizing: border-box; transition: padding-right 0.28s ease; }
body.desmos-open { padding-right: var(--desmos-w); }

#desmos-fab {
  position: fixed; right: 22px; bottom: 22px; z-index: 1200;
  width: 56px; height: 56px; border-radius: 50%;
  border: none; cursor: pointer; color: #fff;
  background: var(--color-primary); box-shadow: 0 4px 14px rgba(0, 0, 0, 0.28);
  font-size: 24px; display: flex; align-items: center; justify-content: center;
  transition: right 0.28s ease, transform 0.15s ease, filter 0.15s ease;
}
#desmos-fab:hover { filter: brightness(1.08); }
#desmos-fab:active { transform: scale(0.94); }
body.desmos-open #desmos-fab { right: calc(var(--desmos-w) + 18px); }

#desmos-panel {
  position: fixed; top: 0; right: 0; height: 100vh; width: var(--desmos-w);
  background: #fff; box-shadow: -4px 0 18px rgba(0, 0, 0, 0.16);
  transform: translateX(100%); transition: transform 0.28s ease;
  z-index: 1100; display: flex; flex-direction: column;
}
body.desmos-open #desmos-panel { transform: translateX(0); }
.desmos-bar {
  flex: 0 0 auto; display: flex; align-items: center; justify-content: space-between;
  padding: 8px 14px; background: var(--color-primary); color: #fff;
  font-size: 14px; font-weight: 600;
}
#desmos-close { background: none; border: none; color: #fff; font-size: 18px; line-height: 1; cursor: pointer; padding: 2px 6px; }
#desmos-close:hover { opacity: 0.8; }
#desmos-calc { flex: 1 1 auto; width: 100%; min-height: 0; }

@media (max-width: 900px) {
  :root { --desmos-w: 100vw; }
  body.desmos-open { padding-right: 0; }
  body.desmos-open #desmos-fab { right: 18px; bottom: 18px; }
}
@media print { #desmos-fab, #desmos-panel { display: none !important; } }

/* ===== Example solution collapse ===== */
.solution-toggle {
  display: inline-flex; align-items: center; gap: 6px;
  margin: 14px 0 6px; padding: 9px 18px;
  background: var(--color-surface); color: var(--color-primary);
  border: 1.5px solid var(--color-primary); border-radius: 6px;
  font-family: inherit; font-size: 14px; font-weight: 600; cursor: pointer;
  transition: background 0.15s;
}
.solution-toggle::after { content: '▾'; font-size: 11px; }
.solution-toggle:hover { background: #f0f4ff; }
.solution-section.solution-collapsed { display: none; }
@media print {
  .solution-toggle { display: none !important; }
  .solution-section.solution-collapsed { display: block !important; }
}