/* PAGE BACKGROUND */
body {
  background: linear-gradient(135deg, #0b1120, #0f172a);
  color: #e2e8f0;
  font-family: Arial, sans-serif;
  margin: 0;
}

/* LAYOUT */
.chapter-layout {
  display: grid;
  grid-template-columns: 3fr 1fr;
  gap: 25px;
  max-width: 1200px;
  margin-left: 40px;
  margin-right: auto;
  padding: 25px 20px 60px;
}

/* LEFT CONTENT */
.lesson-content h1 {
  color: #38bdf8;
  font-size: 2.6rem;
  margin-bottom: 5px;
}

.chapter-subtitle {
  color: #94a3b8;
  margin-bottom: 20px;
}

/* BACK BUTTON */
.back-btn {
  display: inline-block;
  margin-bottom: 15px;
  padding: 10px 16px;
  background: #1e293b;
  color: #38bdf8;
  border-radius: 8px;
  text-decoration: none;
  font-weight: bold;
  transition: 0.2s;
}

.back-btn:hover {
  background: #38bdf8;
  color: #020617;
}

/* VIDEO */
.video-section iframe {
  width: 100%;
  height: 420px;
  border-radius: 14px;
  box-shadow: 0 12px 35px rgba(0,0,0,0.6);
}

/* PREV NEXT BUTTONS */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  margin: 18px 0;
}

.nav-btn {
  padding: 10px 18px;
  background: #1e293b;
  color: #38bdf8;
  border-radius: 8px;
  text-decoration: none;
  font-weight: bold;
  transition: 0.2s;
}

.nav-btn:hover {
  background: #38bdf8;
  color: #020617;
}

/* INFO CARD */
.lesson-info {
  background: #0f172a;
  padding: 18px;
  border-radius: 12px;
  margin-bottom: 20px;
  line-height: 1.6;
  color: #cbd5e1;
  box-shadow: 0 8px 25px rgba(0,0,0,0.5);
}

/* STEPS */
.steps h2 {
  color: #22c55e;
  margin-bottom: 12px;
}

.step-card {
  background: #1e293b;
  padding: 14px;
  border-radius: 10px;
  margin-bottom: 10px;
}

/* SIDEBAR */
.lesson-sidebar {
  position: sticky;
  top: 20px;
  height: fit-content;
}

.sidebar-box {
  background: #0f172a;
  padding: 18px;
  border-radius: 12px;
  margin-bottom: 15px;
  text-align: center;
  box-shadow: 0 8px 25px rgba(0,0,0,0.5);
}

.side-btn {
  display: block;
  margin-top: 10px;
  padding: 10px;
  background: #38bdf8;
  color: #020617;
  border-radius: 8px;
  text-decoration: none;
  font-weight: bold;
}

.side-btn.red {
  background: #ff0000;
  color: white;
}

/* MOBILE RESPONSIVE */
@media (max-width: 900px) {
  .chapter-layout {
    grid-template-columns: 1fr;
    margin-left: auto;
  }

  .lesson-sidebar {
    position: static;
  }

  .video-section iframe {
    height: 240px;
  }
}