body {
      background-color: #e6f0f5;
      font-family: Arial, sans-serif;
      margin: 0;
      padding: 0;
    }

    /* Thanh menu */
    .navbar {
      background-color: #2980b9;
      padding: 10px 0;
      text-align: center;
    }
    .navbar a {
      color: white;
      text-decoration: none;
      margin: 0 15px;
      font-weight: bold;
      transition: 0.3s;
    }
    .navbar a:hover {
      color: #ffeb3b;
    }

    /* Banner */
    .banner {
      width: 100%;
      max-width: 900px;
      margin: 20px auto;
      overflow: hidden;
      border-radius: 8px;
      box-shadow: 0 4px 10px rgba(0,0,0,0.2);
    }
    .slides {
      display: flex;
      transition: transform 1s ease;
    }
    .slides img {
      width: 100%;
      flex: 0 0 100%;
      display: block;
      height: auto;
    }

    /* Danh sách bài tập */
    .content {
      width: 90%;
      max-width: 900px;
      margin: 20px auto;
      display: flex;
      justify-content: center;
      gap: 20px;
    }
    .card {
      flex: 1;
      background: #fff;
      padding: 20px;
      border-radius: 10px;
      text-align: center;
      box-shadow: 0 4px 8px rgba(0,0,0,0.1);
      transition: transform 0.3s, box-shadow 0.3s;
    }
    .card:hover {
      transform: translateY(-5px);
      box-shadow: 0 6px 12px rgba(0,0,0,0.2);
      color:#d35400;
    }
    .card a {
      text-decoration: none;
      font-size: 18px;
      font-weight: bold;
      color: #2980b9;
    }
    .card a:hover {
      color: #d35400;
    }

    footer {
      text-align: center;
      padding: 15px;
      margin-top: 30px;
      background: #2980b9;
      color: white;
    }

body {
      background-color: #e6f0f5;
      font-family: Arial, sans-serif;
      margin: 0;
      padding: 0;
    }

    .navbar {
      background-color: #2980b9;
      padding: 10px 0;
      text-align: center;
    }
    .navbar a {
      color: white;
      text-decoration: none;
      margin: 0 15px;
      font-weight: bold;
      transition: 0.3s;
    }
    .navbar a:hover {
      color: #ffeb3b;
    }

    .banner {
      width: 100%;
      max-width: 900px;
      margin: 20px auto;
      overflow: hidden;
      border-radius: 8px;
      box-shadow: 0 4px 10px rgba(0,0,0,0.2);
    }
    .slides {
      display: flex;
      transition: transform 1s ease;
    }
    .slides img {
      width: 100%;
      flex: 0 0 100%;
      display: block;
    }

    .card {
      width: 90%;
      max-width: 600px;
      margin: 20px auto;
      background: #fff;
      padding: 20px;
      border-radius: 10px;
      box-shadow: 0 4px 8px rgba(0,0,0,0.1);
      cursor: pointer;
    }
    .card h1 {
      color: #2980b9;
      margin-bottom: 15px;
    }

    footer {
      text-align: center;
      padding: 15px;
      margin-top: 30px;
      background: #2980b9;
      color: white;
    }
    .main-box {
  width: 95%;
  max-width: 1000px;
  margin: 30px auto;
  background: #fff;
  border-radius: 12px;
  box-shadow: 0 6px 15px rgba(0,0,0,0.15);
  padding: 20px;
}
    body {
      background-color: #e6f0f5;
      font-family: Arial, sans-serif;
      margin: 0;
      padding: 0;
    }

    .navbar {
      background-color: #2980b9;
      padding: 10px 0;
      text-align: center;
    }
    .navbar a {
      color: white;
      text-decoration: none;
      margin: 0 15px;
      font-weight: bold;
    }
    .navbar a:hover {
      color: #ffeb3b;
    }

    .main-box {
      width: 95%;
      max-width: 1100px;
      margin: 30px auto;
      background: #fff;
      border-radius: 12px;
      box-shadow: 0 6px 15px rgba(0,0,0,0.15);
      padding: 20px;
    }

    .section {
      margin: 30px 0;
      padding: 20px;
      border-radius: 10px;
      background: #f9f9f9;
      box-shadow: 0 3px 6px rgba(0,0,0,0.1);
    }
    .section h1, .section h2 {
      color: #2980b9;
      margin-bottom: 15px;
    }

    .intro {
      display: flex;
      gap: 20px;
      align-items: flex-start;
    }
    .intro img {
      max-width: 300px;
      border-radius: 10px;
    }
    .intro p {
      font-size: 20px;
      line-height: 1.5;
    }

    .gallery img {
      width: 220px;
      height: 220px;
      margin: 10px;
      border-radius: 8px;
      box-shadow: 0 2px 6px rgba(0,0,0,0.2);
    }

    iframe, video {
      border-radius: 10px;
      margin-top: 15px;
      max-width: 100%;
    }

    footer {
      text-align: center;
      padding: 15px;
      margin-top: 30px;
      background: #2980b9;
      color: white;
    }