/* Общие стили для проекта на Bootstrap */
body {
  background: #f8fafc;
}
h1, h2, h3, h4, h5 {
  font-family: 'Segoe UI', Arial, sans-serif;
  font-weight: 700;
}

.lesson-block {
  border: 1px solid #e3f2fd;
  border-radius: 8px;
  margin-bottom: 18px;
  background: #fff;
  box-shadow: 0 2px 8px rgba(26,34,54,0.04);
}
.lesson-title {
  cursor: pointer;
  padding: 14px 18px;
  font-size: 1.15em;
  font-weight: 600;
  color: #1976d2;
  display: flex;
  align-items: center;
  user-select: none;
}
.lesson-title .arrow {
  margin-left: auto;
  transition: transform 0.2s;
}
.lesson-block .lesson-content {
  display: none;
  padding: 0 18px 16px 18px;
}
.lesson-block.open .lesson-content {
  display: block;
}
.lesson-block.open .arrow {
  transform: rotate(90deg);
}