/* 全局 */
body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI",
               Roboto, Helvetica, Arial, sans-serif;
  color: #1a1a1a;
  background: #ffffff;
}

header {
  padding: 70px 20px 40px;
  text-align: center;
  border-bottom: 1px solid #e5e5e5;
}

header h1 { font-size: 42px; margin-bottom: 10px; color: #000000; }
header p { font-size: 20px; color: #555; }

/* 导航栏 北大红 */
.navbar {
  background: #990000; /* 北大红 */
  padding: 15px;
  text-align: center;
}

.navbar a {
  color: white;
  margin: 0 18px;
  text-decoration: none;
  font-weight: 500;
}

.navbar a:hover { color: #ffcccc; }

/* 容器 */
.container {
  max-width: 1200px;
  margin: auto;
  padding: 50px 20px;
}

/* 标题 黑色 */
h2 { color: #000000; text-align: center; }

/* 高亮块 黑色边框 */
.highlight {
  background: #f5f5f5; /* 浅灰背景 */
  padding: 20px;
  border-left: 4px solid #000000;
  margin: 30px 0;
}

/* 页脚 黑色 */
footer {
  text-align: center;
  padding: 40px 20px;
  border-top: 1px solid #e5e5e5;
  color: #000000;
  font-size: 14px;
}

/* 轮播 480x320 */
.carousel-wrapper {
  position: relative;
  width: 100%;
  max-width: 1200px;
  margin: 40px auto;
}

.research-carousel {
  overflow: hidden;
  height: 320px;
}

.carousel-track {
  display: flex;
  gap: 20px;
}

.carousel-item {
  position: relative;
  flex: none;
}

/* 轮播图片 黑色边框 */
.carousel-item img {
  width: 480px;
  height: 320px;
  object-fit: cover;
  border-radius: 0px;
  border: 0px solid #000000; /* 黑色边框 */
  cursor: pointer;
  transition: transform 0.3s ease;
}

.carousel-item img:hover { transform: scale(1.05); }

/* 轮播标题说明 半透明黑 */
.caption {
  position: absolute;
  bottom: 0;
  width: 100%;
  background: rgba(0,0,0,0.7);
  color: white;
  padding: 6px 10px;
  border-radius: 0 0 12px 12px;
  text-align: left;
}

.caption h3 { margin: 0; font-size: 16px; }
.caption p { margin: 2px 0 0; font-size: 12px; }

/* 箭头 黑色半透明 */
.arrow {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  background: rgba(0,0,0,0.7);
  color: white;
  border: none;
  padding: 12px 18px;
  font-size: 28px;
  cursor: pointer;
  border-radius: 5px;
  z-index: 10;
}

.arrow.left { left: 10px; }
.arrow.right { right: 10px; }

/* Modal 放大 */
.modal {
  display: none;
  position: fixed;
  z-index: 9999;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  background: rgba(0,0,0,0.9);
  padding-top: 80px;
}

.modal img {
  display: block;
  margin: auto;
  max-width: 90%;
  max-height: 85vh;
  border-radius: 0px;
  box-shadow: 0 20px 40px rgba(0,0,0,0.6);
  transition: transform 0.3s ease;
}

/* 响应式 */
@media screen and (max-width: 1200px) {
  .carousel-item img { width: 400px; height: 260px; }
  .research-carousel { height: 260px; }
}

@media screen and (max-width: 768px) {
  .carousel-item img { width: 320px; height: 210px; }
  .research-carousel { height: 210px; }
  .arrow { font-size: 24px; padding: 10px 15px; }
}

@media screen and (max-width: 480px) {
  .carousel-item img { width: 240px; height: 160px; }
  .research-carousel { height: 180px; }
  .arrow { font-size: 20px; padding: 8px 12px; }
}