@import url('https://fonts.googleapis.com/css2?family=Montserrat:wght@400;700&display=swap');

body {
  margin: 0;
  font-family: 'Montserrat', sans-serif;
  background: linear-gradient(rgba(10, 10, 10, 0.7), rgba(0, 0, 0, 0.8)),
    url('https://images.pexels.com/photos/36715/pexels-photo.jpg?auto=compress&cs=tinysrgb&dpr=2&h=750&w=1260') no-repeat center center fixed;
  background-size: cover;
  color: #eee;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  padding: 60px 20px;
}

.main-container {
  background-color: rgba(15, 15, 15, 0.85);
  max-width: 850px;
  padding: 40px 50px;
  border-radius: 14px;
  box-shadow: 0 0 35px rgba(0, 0, 0, 0.7);
  animation: fadeSlideIn 1.5s ease forwards;
}

header {
  text-align: center;
  margin-bottom: 28px;
}

h1 {
  font-weight: 700;
  font-size: 3rem;
  letter-spacing: 2px;
  margin-bottom: 12px;
  color: #ff7f50;
  text-shadow: 0 0 15px #ff6347;
}

.back-link {
  font-weight: 600;
  font-size: 1.15rem;
  color: #ff7f50;
  text-decoration: none;
  border-bottom: 2px solid transparent;
  transition: border-color 0.3s ease;
}
.back-link:hover {
  border-bottom: 2px solid #ff7f50;
}

h2 {
  color: #ffa07a;
  border-bottom: 2px solid #ff7f50;
  padding-bottom: 7px;
  margin-top: 30px;
  margin-bottom: 18px;
  font-weight: 700;
}

.definition p,
.concepts ul {
  font-size: 1.2rem;
  line-height: 1.7;
  max-width: 700px;
  margin: 0 auto;
}

.concepts ul {
  list-style-type: square;
  padding-left: 24px;
}

.concepts li {
  margin-bottom: 11px;
}

.video iframe {
  display: block;
  margin: 25px auto;
  width: 100%;
  max-width: 560px;
  height: 315px;
  border-radius: 15px;
  box-shadow: 0 0 20px #ff7f50aa;
}

/* Animation */
@keyframes fadeSlideIn {
  0% {
    opacity: 0;
    transform: translateY(30px);
  }
  100% {
    opacity: 1;
    transform: translateY(0);
  }
}