:root {
    --teal-green: #20c997;
    --deep-teal: #138d75;
    --navy-blue: #001f3f;
    --dark-navy: #001737;
    --light-gray: #f4f4f4;
    --white: #ffffff;
    --dark-bg: #1f1f1f;
    --dark-card: #2c2c2c;
    --light-on-dark: #f0f0f0;
    --muted-gray: #aaa;
  }
  
  * {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
  }
  
  body {
    font-family: 'Segoe UI', sans-serif;
    background-color: var(--light-gray);
    color: var(--navy-blue);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 2rem;
    transition: background 0.3s, color 0.3s;
  }
  
  body.dark {
    background-color: var(--dark-bg);
    color: var(--light-on-dark);
  }
  
  .container {
    background-color: var(--white);
    padding: 2rem;
    border-radius: 20px;
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.1);
    width: 100%;
    max-width: 500px;
    transition: background 0.3s;
  }
  
  body.dark .container {
    background-color: var(--dark-card);
  }
  
  .brand-title {
    font-size: 2rem;
    font-weight: 700;
    text-align: center;
    margin-bottom: 1.5rem;
    background: linear-gradient(to right, #20c997, #138d75, #001f3f);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
  }
  
  .timer-setup {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    margin-bottom: 2rem;
  }
  
  .timer-setup label {
    font-weight: bold;
  }
  
  input[type="datetime-local"] {
    padding: 0.6rem;
    font-size: 1rem;
    border: 1px solid var(--muted-gray);
    border-radius: 10px;
    background-color: var(--white);
    color: var(--navy-blue);
  }
  
  body.dark input[type="datetime-local"] {
    background-color: var(--dark-card);
    color: var(--light-on-dark);
    border: 1px solid var(--muted-gray);
  }
  
  button {
    padding: 0.8rem;
    font-size: 1rem;
    border: none;
    border-radius: 10px;
    background-color: var(--teal-green);
    color: white;
    cursor: pointer;
    transition: background 0.3s;
  }
  
  button:hover {
    background-color: var(--deep-teal);
  }
  
  #countdown-display {
    text-align: center;
    font-size: 2rem;
    display: flex;
    justify-content: space-around;
    margin-bottom: 1.5rem;
  }
  
  #countdown-display div {
    display: flex;
    flex-direction: column;
    align-items: center;
  }
  
  #countdown-display span {
    font-weight: bold;
    font-size: 2.5rem;
  }
  
  #countdown-display small {
    font-size: 0.8rem;
    color: var(--muted-gray);
  }
  
  body.dark #countdown-display small {
    color: #ccc;
  }
  
  @media (max-width: 480px) {
    #countdown-display {
      flex-direction: column;
      gap: 1rem;
    }
  }