/* 全局样式 */
body {
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
}

/* 顶部菜单样式 */
header {
  background-color: #333;
  color: white;
  padding: 10px 0;
}

nav ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
  display: flex;
  justify-content: center;
}

nav ul li {
  margin: 0 15px;
}

nav ul li a {
  color: white;
  text-decoration: none;
}

nav ul li a:hover {
  text-decoration: underline;
}

/* 主要内容部分样式 */
main {
  padding: 20px;
  text-align: center;
}

.course-list {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}

.course-item {
  width: 300px;
  margin: 20px;
  border: 1px solid #ccc;
  border-radius: 5px;
  padding: 10px;
}

.course-item img {
  width: 100%;
  height: auto;
}