.sd-section {
  padding: 76px 28px 58px;
  background: linear-gradient(180deg, #eef3f8 0%, #f5f7fa 100%);
  border-top: 1px solid var(--gray);
  border-bottom: 1px solid var(--gray);
  scroll-margin-top: 66px;
}
.sd-intro {
  max-width: 1080px;
  margin: 0 auto 26px;
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 24px;
}
.sd-intro h2 {
  font-size: clamp(29px, 4vw, 40px);
  line-height: 1.13;
  letter-spacing: -.035em;
  margin: 12px 0;
}
.sd-intro p {
  max-width: 590px;
  color: var(--muted);
  font-size: 15px;
  line-height: 1.65;
}
.sd-preview-note {
  flex: 0 0 auto;
  font-size: 11px;
  font-weight: 700;
  color: var(--steel);
  background: #e4edf5;
  border: 1px solid #cbdde9;
  border-radius: 99px;
  padding: 7px 12px;
}
#student-demo-frame {
  display: block;
  max-width: 1080px;
  width: 100%;
  min-height: 720px;
  height: 720px;
  border: 0;
  margin: 0 auto;
  overflow: hidden;
}
#teachers, #course-developers { scroll-margin-top: 66px; }
.sd-developer-section { border-top: 1px solid var(--gray); }
@media(max-width: 760px) {
  .nav-inner { padding: 12px 18px; align-items: flex-start; gap: 10px; }
  .nav-links { gap: 10px; flex-wrap: wrap; justify-content: flex-end; font-size: 11px; }
  .nav-links .btn { padding: 7px 10px; font-size: 11px; }
  .sd-section { padding: 52px 12px 34px; }
  .sd-intro { display: block; padding: 0 12px; }
  .sd-preview-note { display: inline-block; margin-top: 16px; }
  #student-demo-frame { min-height: 960px; height: 960px; }
}
@media(max-width: 480px) {
  .nav-inner { display: block; }
  .nav-links { justify-content: flex-start; margin-top: 8px; }
  .nav-links .btn { display: none; }
}