*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: "Segoe UI", system-ui, -apple-system, sans-serif;
  background: #f5f3ef;
  color: #2c2c2c;
  line-height: 1.7;
}

header {
  text-align: center;
  padding: 3rem 1rem 2rem;
  background: #fff;
  border-bottom: 1px solid #e0dcd6;
}

header h1 {
  font-size: 2.2rem;
  font-weight: 700;
  color: #1a1a1a;
}

header .subtitle {
  font-size: 1.1rem;
  color: #666;
  margin-top: 0.4rem;
}

nav {
  margin-top: 1.2rem;
  display: flex;
  justify-content: center;
  gap: 0.5rem;
}

.nav-link {
  display: inline-block;
  padding: 0.5rem 1.5rem;
  text-decoration: none;
  color: #555;
  border: 1px solid #ddd;
  border-radius: 4px;
  font-size: 0.95rem;
  transition: background 0.15s, color 0.15s;
}

.nav-link:hover {
  background: #f0ece4;
}

.nav-link.active {
  background: #2c2c2c;
  color: #fff;
  border-color: #2c2c2c;
}

.content-section {
  display: none;
}

.content-section.active {
  display: block;
}

.process-intro {
  text-align: center;
  margin-bottom: 2.5rem;
}

.process-intro h2 {
  font-size: 1.8rem;
  color: #1a1a1a;
  margin-bottom: 0.8rem;
}

.process-intro .intro-text {
  font-size: 1.05rem;
  color: #555;
  max-width: 720px;
  margin: 0 auto;
  line-height: 1.8;
}

main {
  max-width: 960px;
  margin: 0 auto;
  padding: 2rem 1rem 4rem;
}

.lesson {
  background: #fff;
  border-radius: 8px;
  margin-bottom: 2.5rem;
  padding: 2rem;
  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.06);
}

.lesson img {
  display: block;
  max-width: 100%;
  width: 900px;
  margin: 0 auto 1.5rem;
  border-radius: 6px;
  border: 1px solid #e0dcd6;
}

.lesson h2 {
  font-size: 1.5rem;
  margin-bottom: 1rem;
  color: #1a1a1a;
}

.lesson p {
  margin-bottom: 1rem;
  font-size: 1rem;
  color: #3a3a3a;
}

.lesson .project-lesson {
  background: #faf8f4;
  border-left: 4px solid #c9a84c;
  padding: 1rem 1.2rem;
  border-radius: 0 6px 6px 0;
  margin-top: 0.5rem;
}

.lesson .project-lesson h3 {
  font-size: 0.9rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: #8a7530;
  margin-bottom: 0.5rem;
}

footer {
  text-align: center;
  padding: 2rem 1rem;
  color: #999;
  font-size: 0.9rem;
  border-top: 1px solid #e0dcd6;
}

@media (max-width: 640px) {
  header h1 {
    font-size: 1.6rem;
  }

  .lesson {
    padding: 1.2rem;
  }

  .lesson h2 {
    font-size: 1.25rem;
  }
}