:root {
      --bg: #f2f2f2;
      --paper: #ffffff;
      --text: #171717;
      --line: #d0d0d0;
      --soft: #f6f6f6;
      --nav-fill: rgba(0,0,0,0.045);
      --nav-fill-hover: rgba(0,0,0,0.085);
      --division-line: #333;
    }

    * {
      box-sizing: border-box;
      border-radius: 0 !important;
    }

    html, body {
      margin: 0;
      padding: 0;
      background: var(--bg);
      color: var(--text);
      font-family: Arial, Helvetica, sans-serif;
      line-height: 1.5;
    }

    main {
      width: min(1180px, calc(100% - 112px));
      margin: 24px auto 48px;
    }

    .workspace {
      position: relative;
      background: var(--paper);
      border: 1px solid var(--line);
      padding: 24px;
    }

    .columns {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 36px;
      align-items: start;
    }

    .workspace::after {
      content: "";
      position: absolute;
      left: 50%;
      top: 12px;
      bottom: 12px;
      width: 1px;
      background: var(--line);
      transform: translateX(-0.5px);
      pointer-events: none;
    }

    .column { min-width: 0; }

    .explanation {
      border: 1px solid #d8d8d8;
      background: var(--soft);
      padding: 12px 14px;
      margin: 0 0 24px;
      color: #555;
      text-align: center;
      font-size: 0.78rem;
      line-height: 1.5;
    }

    .explanation h2 {
      margin: 0 0 0.8em;
      font-size: 0.84rem;
      font-weight: 600;
      color: #555;
    }

    .explanation h3 {
      margin: 1.1em 0 0.5em;
      font-size: 0.8rem;
      font-weight: 600;
      color: #555;
    }

    .explanation p {
      margin: 0.75em 0;
    }

    .explanation .math-line {
      margin: 0.45em 0;
    }

    .explanation mjx-container[display="true"] {
      margin: 0.85em 0 !important;
    }

    .question-title {
      margin: 0 0 12px;
      font-size: 1.12rem;
      font-weight: 700;
      text-align: left;
    }

    .subq {
      position: relative;
      margin: 0 0 10px;
      text-align: left;
    }

    .subq-row {
      display: flex;
      align-items: baseline;
      gap: 8px;
      flex-wrap: wrap;
    }

    .label {
      min-width: 1.4em;
      font-weight: 700;
    }

    .question {
      position: relative;
      display: grid;
      grid-template-columns: 1.8em 1fr;
      column-gap: 10px;
      margin: 0 0 10px;
      text-align: left;
      break-inside: avoid;
    }

    .question-number {
      grid-column: 1;
      font-weight: 700;
      align-self: start;
    }

    .question-body {
      grid-column: 2;
      min-width: 0;
    }

    .question-line {
      display: block;
      margin: 0;
    }


    

    .question-line + .question-line {
      margin-top: 0;
    }

    .question-line.line-math + .question-line.line-math,
    .question-line.line-math + .question-line.line-table,
    .question-line.line-table + .question-line.line-math {
      margin-top: 6px;
    }

    .question-line.line-table + .question-line.line-table {
      margin-top: 0;
    }

    .scratch {
      min-height: 100px;
    }

    .answer-button {
      position: absolute;
      right: 0;
      bottom: 0;
      z-index: 2;
      border: 1px solid #c8c8c8;
      background: #f7f7f7;
      color: #666;
      padding: 5px 9px;
      font: inherit;
      font-size: 0.84rem;
      min-width: 94px;
      width: auto;
      white-space: nowrap;
      text-align: center;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      justify-content: center;
    }

    .answer-button:hover {
      color: #222;
      background: #eeeeee;
      border-color: #a9a9a9;
    }

    .answer-button.revealed {
      color: #222;
      background: #f1f1f1;
      font-weight: 400;
    }

    .answer-button {
      position: absolute;
    }

    .answer-label,
    .answer-value {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      white-space: nowrap;
    }

    .answer-label {
      font-weight: 400;
    }

    .answer-value {
      font-weight: 700;
      position: absolute;
      visibility: hidden;
      pointer-events: none;
    }

    .answer-button.revealed .answer-label {
      position: absolute;
      visibility: hidden;
      pointer-events: none;
    }

    .answer-button.revealed .answer-value {
      position: static;
      visibility: visible;
      pointer-events: auto;
    }

    .q1-answer-anchor {
      position: relative;
      height: 0;
    }

    .question-gap {
      height: 24px;
    }

    .page-nav {
      position: fixed;
      top: 0;
      bottom: 0;
      width: 44px;
      background: var(--nav-fill);
      text-decoration: none;
      display: flex;
      align-items: center;
      justify-content: center;
      z-index: 1000;
    }

    .page-nav:hover { background: var(--nav-fill-hover); }
    .page-nav.prev { left: 0; }
    .page-nav.next { right: 0; }

    .page-nav .triangle {
      width: 0;
      height: 0;
      border-top: 8px solid transparent;
      border-bottom: 8px solid transparent;
      opacity: 0.62;
    }

    .page-nav.prev .triangle { border-right: 10px solid #444; }
    .page-nav.next .triangle { border-left: 10px solid #444; }

    /* division layout for page 8 */
    .division-figure {
      display: inline-flex;
      flex-direction: column;
      align-items: flex-start;
      vertical-align: middle;
    }

    .division-top, .division-bottom {
      border-collapse: collapse;
      border-spacing: 0;
      table-layout: auto;
    }

    .division-top td, .division-bottom td {
      padding: 0 8px;
      text-align: center;
      vertical-align: middle;
      white-space: nowrap;
    }

    .division-top .dividend {
      border-bottom: 1px solid var(--division-line);
    }

    .division-top .divisor,
    .division-top .quotient {
      border-left: 1px solid var(--division-line);
    }

    .division-top .quotient {
      border-top: 1px solid var(--division-line);
    }

    .division-top .leftbottom {
      text-align: left;
      padding-left: 0;
    }

    .division-bottom {
      margin-top: 4px;
    }

    .division-bottom .remainder {
      border-top: 1px solid var(--division-line);
      text-align: center;
    }

    .prop9-list {
      margin: 10px 0 0;
      padding: 0;
      list-style: none;
      text-align: left;
    }

    .prop9-list li {
      margin: 8px 0;
    }

    .prop9-list .sq {
      display: inline-block;
      width: 0.65em;
      margin-right: 8px;
    }

    .answer-chip {
      display: inline-block;
      border: 1px solid #bcbcbc;
      padding: 3px 10px;
      background: #fff;
      margin-left: 12px;
      white-space: nowrap;
    }


    /* Multiple-choice layout:
       each option stays intact; only the gaps BETWEEN whole options may expand. */
    .choices {
      display: block;
      width: 100%;
      margin-top: 16px;
    }

    .choice-row {
      display: flex;
      width: 100%;
      align-items: baseline;
    }

    .choice-row.fill {
      justify-content: space-between;
    }

    .choice-row.center {
      justify-content: center;
      gap: 34px;
    }

    .choice-row + .choice-row {
      margin-top: 10px;
    }

    .choice-option {
      display: inline-block;
      flex: 0 0 auto;
      white-space: nowrap;
    }

    /* Test pages only: subtle graph-paper background, roughly 1 cm spacing. */
    .workspace.test-page {
      background-color: #fff;
      background-image:
        linear-gradient(to right, rgba(88, 108, 128, 0.055) 1px, transparent 1px),
        linear-gradient(to bottom, rgba(88, 108, 128, 0.055) 1px, transparent 1px);
      background-size: 38px 38px;
    }

    

    
    }

  






@page {
  size: A4 portrait;
  margin: 0;
}
















    .site-topbar {
      position: sticky;
      top: 0;
      z-index: 3000;
      height: 42px;
      display: flex;
      align-items: center;
      gap: 28px;
      padding: 0 18px;
      background: rgba(255,255,255,0.97);
      border-bottom: 1px solid rgba(0,0,0,0.08);
      backdrop-filter: blur(5px);
    }

    .site-name {
      color: #2d2d2d;
      text-decoration: none;
      font-size: 0.92rem;
      font-weight: 600;
      white-space: nowrap;
    }

    .nav-trigger {
      appearance: none;
      border: 0;
      outline: 0;
      margin: 0;
      padding: 7px 3px;
      background: transparent;
      color: #3f3f3f;
      font: inherit;
      font-size: 0.88rem;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 7px;
    }

    .nav-trigger:hover,
    .nav-trigger[aria-expanded="true"] {
      background: rgba(0,0,0,0.045);
    }

    .nav-caret {
      width: 0;
      height: 0;
      border-left: 4px solid transparent;
      border-right: 4px solid transparent;
      border-top: 5px solid currentColor;
      opacity: 0.65;
    }

    .nav-wrap {
      position: relative;
    }

    .nav-popup {
      position: absolute;
      top: calc(100% + 7px);
      left: 0;
      z-index: 3100;
      display: none;
      padding: 12px;
      background: #fff;
      box-shadow: 0 7px 24px rgba(0,0,0,0.14);
      min-width: 420px;
      max-width: min(860px, calc(100vw - 24px));
    }

    .nav-popup.open {
      display: block;
    }

    .chapter-grid {
      display: grid;
      grid-auto-flow: column;
      grid-template-rows: repeat(10, auto);
      grid-template-columns: repeat(3, minmax(185px, 1fr));
      gap: 3px 8px;
    }

    .section-grid {
      display: grid;
      grid-auto-flow: column;
      grid-template-rows: repeat(7, auto);
      grid-auto-columns: minmax(105px, 1fr);
      gap: 3px 10px;
      min-width: 470px;
    }

    .popup-item {
      display: block;
      padding: 7px 9px;
      color: #444;
      text-decoration: none;
      font-size: 0.84rem;
      line-height: 1.25;
      background: transparent;
    }

    .popup-item:hover {
      background: rgba(0,0,0,0.055);
    }

    .popup-item.current {
      background: rgba(0,0,0,0.08);
      color: #222;
      font-weight: 600;
    }

    .popup-item.disabled {
      color: #9b9b9b;
      cursor: default;
    }

    .popup-item.disabled:hover {
      background: transparent;
    }

    @media (max-width: 760px) {
      .site-topbar {
        gap: 12px;
        padding: 0 10px;
      }

      .site-name {
        font-size: 0.84rem;
      }

      .chapter-grid {
        grid-auto-flow: column;
        grid-template-rows: repeat(15, auto);
        grid-template-columns: repeat(2, minmax(145px, 1fr));
      }

      .section-grid {
        grid-template-rows: repeat(9, auto);
        min-width: min(470px, calc(100vw - 24px));
      }

      .nav-popup {
        position: fixed;
        left: 12px;
        right: 12px;
        top: 48px;
        max-width: none;
        min-width: 0;
        max-height: calc(100vh - 60px);
        overflow: auto;
      }
    }

    


.sign-chart{border-collapse:collapse;margin:10px auto;min-width:280px;text-align:center;color:#444;font-size:.88em}
.sign-chart th,.sign-chart td{padding:4px 8px;font-weight:400}
.sign-chart tr:nth-child(2) th,.sign-chart tr:nth-child(2) td{border-top:1px solid #666}
.sign-chart th{width:42px}.root-label{min-width:34px}.root-cell{font-size:1.05em}
.parabola-pair{display:flex;justify-content:center;gap:18px;margin:9px 0 12px;flex-wrap:wrap}
.parabola-svg{width:145px;height:96px;overflow:visible}.p-axis{stroke:#777;stroke-width:1}.p-curve{fill:none;stroke:#444;stroke-width:1.7}.p-label{font:10px Arial,sans-serif;fill:#555}
.source-example{margin-top:14px;padding-top:8px;border-top:1px solid rgba(0,0,0,.08)}.source-example h3{margin:6px 0 8px;font-size:.84rem}