.course-nav{
    position:sticky; top:0; z-index:1000;
    background:rgba(245,243,235,.94); backdrop-filter:blur(12px);
    border-bottom:1px solid rgba(36,52,49,.10);
  }
  .course-nav-inner{
    width:min(100%,960px); margin:0 auto; padding:10px 16px;
    display:flex; align-items:center; gap:10px;
  }
  .course-brand{font-weight:800; color:#243431; white-space:nowrap; margin-right:auto}
  .course-tabs{display:flex; gap:8px; overflow-x:auto; scrollbar-width:none}
  .course-tabs::-webkit-scrollbar{display:none}
  .course-tab{
    border:1px solid #d6d8d0; border-radius:999px; background:#fffdf8;
    color:#53635f; padding:9px 14px; font-weight:800; cursor:pointer; white-space:nowrap;
  }
  .course-tab.active{background:#243431;color:#fffdf8;border-color:#243431}
  #chapter1Pane[hidden],#chapter2Pane[hidden]{display:none!important}
  .chapter03-shell{width:min(100%,980px);margin:0 auto;padding:34px 18px 42px}
  .chapter03-head{padding:0 8px 18px}
  .chapter03-kicker{margin:0 0 8px;color:#4c8580;font-size:.82rem;font-weight:800;letter-spacing:.14em}
  .chapter03-head h1{margin:0;font-size:clamp(2rem,7vw,3.4rem);line-height:1.15}
  .chapter03-head p{margin:15px 0 0;color:#6f7c78;line-height:1.8}
  .chapter03-card{overflow:hidden;border:1px solid rgba(36,52,49,.09);border-radius:30px;background:#fffdf8;box-shadow:0 22px 60px rgba(49,65,60,.09)}
  .chapter03-frame{display:block;width:100%;height:1040px;border:0;background:#fffdf8}
  @media(max-width:760px){
    .course-nav-inner{align-items:flex-start;flex-direction:column;padding:8px 10px}
    .course-brand{font-size:.9rem}
    .course-tabs{width:100%}
    .course-tab{font-size:.78rem;padding:8px 11px}
    .chapter03-shell{padding:24px 10px 30px}
    .chapter03-card{border-radius:24px}
    .chapter03-frame{height:900px}
  }
  @media(max-width:430px){
    .chapter03-frame{height:820px}
  }