.shell {
  min-height: 100vh;
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
}

.rail {
  position: sticky;
  top: 0;
  height: 100vh;
  padding: 28px 22px;
  border-right: 1px solid var(--line);
  display: flex;
  flex-direction: column;
  background: rgba(245, 243, 237, .88);
  backdrop-filter: blur(18px);
  z-index: 5;
}

.brand {
  display: flex;
  gap: 12px;
  align-items: center;
  font-size: 18px;
  font-weight: 800;
}

.brand-mark {
  width: 42px;
  height: 42px;
  border-radius: 15px;
  display: grid;
  place-items: center;
  background: var(--ink);
  color: #fff;
  box-shadow: 0 10px 24px rgba(0, 0, 0, .15);
}

.brand small {
  display: block;
  margin-top: 3px;
  color: var(--muted);
  font-size: 10px;
  letter-spacing: .16em;
}

.rail-note {
  margin-top: 30px;
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: 20px;
  background: var(--white);
  color: var(--muted);
  font-size: 13px;
  line-height: 1.7;
}

.steps {
  display: grid;
  gap: 8px;
  margin-top: 24px;
}

.step {
  display: flex;
  gap: 12px;
  align-items: center;
  padding: 12px;
  border-radius: 16px;
  color: var(--muted);
  font-size: 13px;
}

.step.active {
  background: var(--green-2);
  color: var(--ink);
  font-weight: 700;
}

.step-num {
  width: 26px;
  height: 26px;
  border: 1px solid var(--line);
  border-radius: 50%;
  display: grid;
  place-items: center;
  font-size: 11px;
}

.step.active .step-num {
  border-color: var(--green);
  background: var(--green);
  color: #fff;
}

.rail-foot {
  margin-top: auto;
  color: var(--muted);
  font-size: 11px;
  line-height: 1.7;
}

.rail-foot b {
  color: var(--ink);
}

main {
  min-width: 0;
  padding: 34px clamp(22px, 5vw, 76px) 90px;
}

.topbar {
  max-width: 1050px;
  margin: 0 auto 30px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
}

.top-actions {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.learning-actions {
  display: grid;
  width: 160px;
  gap: 10px;
  justify-items: stretch;
}

.learning-actions .ghost-btn {
  width: 100%;
}

.view {
  max-width: 1050px;
  margin: 0 auto;
  animation: up .38s ease both;
}

.hero {
  display: grid;
  grid-template-columns: 1.08fr .92fr;
  gap: 32px;
  align-items: stretch;
}

.hero-copy {
  padding: 36px 0;
}

.hero h1 {
  max-width: 800px;
  margin: 18px 0 24px;
  font-size: clamp(46px, 7vw, 90px);
  line-height: .96;
  letter-spacing: 0;
}

.hero h1 em {
  color: var(--green);
  font-family: Georgia, serif;
  font-weight: 400;
}

.hero-copy p {
  max-width: 620px;
  color: var(--muted);
  font-size: 17px;
  line-height: 1.9;
}

.detail-layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 330px;
  gap: 18px;
}

.side-stack {
  display: grid;
  gap: 14px;
  align-content: start;
}

.mobile-nav {
  display: none;
}

@media (max-width: 860px) {
  .shell {
    display: block;
  }

  .rail {
    display: none;
  }

  main {
    padding: 22px 16px calc(150px + var(--safe-bottom));
  }

  .topbar {
    margin-bottom: 18px;
    align-items: flex-start;
  }

  .learning-actions {
    width: 148px;
  }

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

  .hero-copy {
    padding: 22px 0 4px;
  }

  .hero h1 {
    font-size: 54px;
  }

  .feature-grid,
  .meta-grid,
  .detail-layout {
    grid-template-columns: 1fr;
  }

  .feature {
    display: grid;
    grid-template-columns: 42px 1fr;
    column-gap: 8px;
  }

  .feature h3 {
    margin: 3px 0 6px;
  }

  .feature p {
    grid-column: 2;
  }

  .page-head {
    display: block;
  }

  .head-actions {
    margin-top: 16px;
  }

  .mobile-nav {
    position: fixed;
    left: 12px;
    right: 12px;
    bottom: calc(10px + var(--safe-bottom));
    z-index: 10;
    display: flex;
    padding: 7px;
    border-radius: 18px;
    background: rgba(23, 24, 21, .94);
    backdrop-filter: blur(16px);
    box-shadow: 0 12px 36px rgba(0, 0, 0, .22);
  }

  .mobile-nav button {
    flex: 1;
    border: 0;
    border-radius: 12px;
    padding: 10px 5px;
    background: transparent;
    color: rgba(255, 255, 255, .55);
    font-size: 10px;
  }

  .mobile-nav button.active {
    background: #fff;
    color: var(--ink);
    font-weight: 800;
  }
}

@media (max-width: 560px) {
  .topbar {
    display: grid;
  }

  .learning-actions {
    width: 100%;
  }

}