/* Reset mặc định */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
  }
  
  
  body {
    font-family: 'Roboto', sans-serif;
    line-height: 1.6;
    background: linear-gradient(to bottom, #6a11cb, #2575fc); /* Gradient nền chính */
    color: #333;
    padding: 0 1rem;
  }
  
  
  /* Container chính */
  .login-container, .dashboard-container, .exercise-container {
    max-width: 500px;
    width: 90%;
    margin: 20px auto;
    padding: 30px;
    background: #ffffff;
    border-radius: 16px; /* Bo góc lớn hơn */
    border: 1px solid #e0e0e0; /* Đường viền nhạt */
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.15); /* Bóng đổ mềm */
  }
  
  h1 {
    font-size: 2.5rem;
    margin-bottom: 1.5rem;
    text-align: center;
  }
  .card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); /* Tự động điều chỉnh số cột */
    gap: 1.5rem;
    margin-top: 2rem;
  }
  
  .card {
    background: rgba(255, 255, 255, 0.15); /* Nền trong suốt nhẹ */
    border-radius: 10px;
    padding: 1rem;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
  }
  
  .card:hover {
    transform: translateY(-5px); /* Hiệu ứng nổi lên khi hover */
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.3);
  }
  
  .card h3 {
    font-size: 1.25rem;
    margin-bottom: 1rem;
  }
  
  .card button {
    background: #2575fc;
    color: #fff;
    border: none;
    padding: 0.5rem 1rem;
    border-radius: 5px;
    cursor: pointer;
    font-size: 1rem;
    transition: background 0.3s ease;
  }
  
  .card button:hover {
    background: #6a11cb; /* Đổi màu khi hover */
  }
  
  .lesson-container {
    display: flex;
    flex-direction: row;
    justify-content: space-between;
    background: rgba(255, 255, 255, 0.1);
    border-radius: 15px;
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.2);
    width: 90%;
    max-width: 1000px;
    padding: 2rem;
    gap: 2rem;
  }
  
  .sidebar {
    flex: 1;
    background: rgba(255, 255, 255, 0.15);
    border-radius: 10px;
    padding: 1rem;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
  }
  
  .sidebar ul {
    list-style: none;
  }
  
  .sidebar ul li {
    margin-bottom: 1rem;
  }
  
  .sidebar ul li a {
    color: #fff;
    text-decoration: none;
    font-size: 1rem;
  }
  
  .sidebar ul li a:hover {
    text-decoration: underline;
  }
  
  .content {
    flex: 2;
    background: rgba(255, 255, 255, 0.15);
    border-radius: 10px;
    padding: 1.5rem;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
  }
  
  .back-button {
    display: inline-block;
    margin-bottom: 1rem;
    color: #fff;
    text-decoration: none;
    font-size: 1rem;
    background: #2575fc;
    padding: 0.5rem 1rem;
    border-radius: 5px;
    transition: background 0.3s ease;
  }
  
  .back-button:hover {
    background: #6a11cb;
  }
  /* Hiệu ứng fade-in */
.fade-in {
    animation: fadeIn 0.5s ease-in-out;
  }
  
  @keyframes fadeIn {
    from {
      opacity: 0;
      transform: translateY(20px);
    }
    to {
      opacity: 1;
      transform: translateY(0);
    }
  }
  /* Responsive cho màn hình nhỏ */
@media (max-width: 768px) {
    .card-grid {
      grid-template-columns: 1fr; /* Hiển thị một cột */
    }
  
    .lesson-container {
      flex-direction: column; /* Đổi từ hàng ngang sang hàng dọc */
    }
  
    .sidebar {
      margin-bottom: 1rem;
    }
  }
  
  @media (max-width: 480px) {
    h1 {
      font-size: 2rem;
    }
  
    .card button {
      font-size: 0.9rem;
      padding: 0.4rem 0.8rem;
    }
  }
  .sidebar ul li a {
    position: relative;
    padding-left: 1.5rem;
    transition: color 0.3s ease, padding-left 0.3s ease;
  }
  
  .sidebar ul li a:hover {
    color: #6a11cb;
    padding-left: 2rem;
  }
  
  .sidebar ul li a::before {
    content: '▶';
    position: absolute;
    left: 0;
    font-size: 0.9rem;
    color: #fff;
    transition: transform 0.3s ease;
  }
  
  .sidebar ul li a:hover::before {
    transform: translateX(5px);
    color: #6a11cb;
  }
  .card button {
    position: relative;
    overflow: hidden;
  }
  
  .ripple {
    position: absolute;
    width: 20px;
    height: 20px;
    background: rgba(255, 255, 255, 0.5);
    border-radius: 50%;
    transform: scale(0);
    animation: rippleEffect 0.6s ease-out;
    pointer-events: none;
  }
  
  @keyframes rippleEffect {
    to {
      transform: scale(10);
      opacity: 0;
    }
  }
  body {
    font-family: 'Roboto', sans-serif;
  }
  
  h1, h2, h3 {
    font-weight: 700;
  }
  
  p, ul li {
    font-weight: 400;
    line-height: 1.6;
  }