body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #f4f7f6;
    color: #333;
    margin: 0;
    padding: 20px;
    display: flex;
    justify-content: center;
  }
  
  .container {
    max-width: 600px;
    width: 100%;
  }
  
  header {
    text-align: center;
    margin-bottom: 30px;
  }
  
  h1 {
    color: #2c3e50;
    margin-bottom: 5px;
  }
  
  .card {
    background: white;
    padding: 25px;
    border-radius: 10px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.05);
    margin-bottom: 25px;
    border-left: 6px solid #3498db;
  }
  
  .card:nth-child(3) { border-color: #e74c3c; } /* Eq 2 color */
  .card:nth-child(4) { border-color: #2ecc71; } /* Eq 3 color */
  
  h2 {
    margin-top: 0;
    font-size: 1.2rem;
    color: #2c3e50;
  }
  
  .equation-text {
    font-family: 'Courier New', Courier, monospace;
    font-size: 1.5rem;
    font-weight: bold;
    background: #ecf0f1;
    padding: 10px;
    text-align: center;
    border-radius: 5px;
    margin-bottom: 10px;
    color: #2980b9;
  }
  
  .desc {
    font-size: 0.9rem;
    color: #7f8c8d;
    margin-bottom: 15px;
  }
  
  .inputs {
    display: flex;
    flex-direction: column;
    gap: 12px;
    margin-bottom: 20px;
  }
  
  label {
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-weight: bold;
    font-size: 0.95rem;
  }
  
  input {
    width: 50%;
    padding: 10px;
    border: 1px solid #ccc;
    border-radius: 5px;
    font-size: 1rem;
  }
  
  button {
    width: 100%;
    padding: 12px;
    background: #3498db;
    color: white;
    border: none;
    border-radius: 5px;
    font-size: 1rem;
    font-weight: bold;
    cursor: pointer;
    transition: 0.3s;
  }
  
  button:hover {
    background: #2980b9;
  }
  
  .result {
    margin-top: 15px;
    padding: 15px;
    background: #e8f8f5;
    color: #16a085;
    border: 1px solid #1abc9c;
    border-radius: 5px;
    text-align: center;
    font-weight: bold;
    font-size: 1.1rem;
  }
  
  .error {
    background: #fdedec;
    color: #c0392b;
    border-color: #e74c3c;
  }