body {
  margin: 0;
  font-family: Arial, sans-serif;
  background: #eef2f6;
}

.layout {
  display: flex;
  min-height: 100vh;
}

.sidebar {
  width: 360px;
  background: #163b6d;
  color: white;
  padding: 40px 24px;
  box-sizing: border-box;
  overflow: hidden;
  flex-shrink: 0;
}

.sidebar h1 {
  font-size: 34px;
  line-height: 1.1;
  margin: 0 0 20px 0;
  font-weight: 800;
  word-break: break-word;
}

.sidebar p {
  font-size: 20px;
  margin: 0 0 28px 0;
}

.menu-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

.menu-list li {
  margin-bottom: 14px;
}

.menu-list button {
  width: 100%;
  border: none;
  background: #3f73b8;
  color: white;
  padding: 18px 20px;
  border-radius: 14px;
  font-size: 18px;
  text-align: left;
  cursor: pointer;
  transition: background 0.2s ease;
}

.menu-list button:hover {
  background: #4b82cc;
}

.content {
  flex: 1;
  padding: 40px;
  box-sizing: border-box;
}

#mainContent {
  max-width: 980px;
  margin: 0 auto;
  background: #f8fafc;
  border-radius: 24px;
  padding: 40px;
  box-sizing: border-box;
}

.main-title {
  color: #173763;
  font-size: 34px;
  line-height: 1.25;
  margin: 0 0 12px 0;
}

.subtitle {
  color: #8a94a6;
  font-style: italic;
  font-size: 18px;
  margin: 0 0 24px 0;
}

.explanation-box {
  background: #f1f5f9;
  border-left: 5px solid #2f67aa;
  padding: 24px;
  border-radius: 10px;
  margin: 24px 0;
  white-space: pre-line;
  font-size: 16px;
  line-height: 1.8;
}

.image-card {
  margin: 28px 0;
}

.image-card img {
  width: 100%;
  border-radius: 18px;
  display: block;
}

.file-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
  border: 1px solid #d6dde6;
  background: white;
  padding: 18px 20px;
  border-radius: 14px;
  margin-top: 14px;
  flex-wrap: wrap;
}

.download-btn {
  background: #2f6db3;
  color: white;
  text-decoration: none;
  padding: 12px 18px;
  border-radius: 10px;
  font-weight: 600;
}

.download-btn:hover {
  background: #255892;
}

@media (max-width: 900px) {
  .layout {
    flex-direction: column;
  }

  .sidebar {
    width: 100%;
    padding: 28px 20px;
  }

  .sidebar h1 {
    font-size: 28px;
  }

  .sidebar p {
    font-size: 18px;
  }

  .content {
    padding: 20px;
  }

  #mainContent {
    padding: 24px;
  }

  .main-title {
    font-size: 28px;
  }
}
.section-small-title {
  margin-top: 28px;
  margin-bottom: 14px;
  color: #7d8ba3;
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 1px;
}

.video-card {
  margin: 20px 0 30px 0;
}

.video-card iframe {
  width: 100%;
  height: 500px;
  border-radius: 18px;
  display: block;
}