* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Inter', sans-serif;
  }
  
  body {
    background-color: #f6f8fa;
    color: #333;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
  }
  
  .nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
  }
  
  nav a {
    color: white;
    margin-left: 20px;
    text-decoration: none;
  }
  
  nav a.active {
    text-decoration: underline;
  }
  
  main {
    max-width: 700px;
    margin: 2rem auto;
    text-align: center;
    padding: 1rem;
  }
  
  button {
    margin: 0.5rem;
    padding: 0.6rem 1.2rem;
    font-size: 1rem;
    border: none;
    border-radius: 8px;
    background-color: #264ef7;
    color: white;
    cursor: pointer;
  }
  
  .timer {
    font-size: 3rem;
    margin: 2rem 0 1rem;
    border: 4px solid #264ef7;
    border-radius: 50%;
    width: 150px;
    height: 150px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    margin-inline: auto;
  }
  
  main.timer-container {
    flex: 1;
    max-width: 500px;
    margin: 40px auto;
    background: white;
    padding: 30px;
    border-radius: 12px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.1);
    text-align: center;
  }
  
  .countdown-display {
    font-size: 48px;
    font-weight: 700;
    margin: 20px 0;
    color: #5236ff;
  }
  
  .input-section {
    display: flex;
    flex-direction: column;
    gap: 10px;
    margin-bottom: 20px;
  }
  
  .input-section input {
    padding: 10px;
    font-size: 16px;
    border: 1px solid #ccc;
    border-radius: 8px;
  }
  
  .button-group {
    display: flex;
    justify-content: center;
    gap: 15px;
  }
  
  button {
    padding: 10px 20px;
    border: none;
    border-radius: 8px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    color: white;
    transition: background 0.3s;
  }
  
  button.start {
    background-color: #28c76f;
  }
  
  button.pause {
    background-color: #ff9f43;
  }
  
  button.reset {
    background-color: #ea5455;
  }
  
  @media (max-width: 600px) {
    header {
      flex-direction: column;
      align-items: flex-start;
    }
  
    header nav {
      flex-direction: column;
      align-items: flex-start;
      gap: 0.5rem;
    }
  
    .timer {
      width: 120px;
      height: 120px;
      font-size: 2.5rem;
    }
  
    button {
      width: 100%;
      max-width: 250px;
    }
  }