:root {
    --green: #20c997;
    --deep-teal: #138d75;
    --navy: #001f3f;
    --dark-navy: #001737;
    --light-gray: #f4f4f4;
    --white: #ffffff;
    --dark-bg: #1f1f1f;
    --dark-card: #2c2c2c;
    --light-text: #f0f0f0;
    --muted: #aaa;
    --shadow: rgba(0, 0, 0, 0.1);
  }
  
  * {
    box-sizing: border-box;
  }
  
  body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: var(--light-gray);
    color: #333;
    margin: 0;
    padding: 0;
    transition: background-color 0.3s, color 0.3s;
  }
  
  .dark-mode {
    background-color: var(--dark-bg);
    color: var(--light-text);
  }
  
  header {
    text-align: center;
    padding: 20px;
    background-color: var(--white);
    box-shadow: 0 2px 5px var(--shadow);
  }
  
  .dark-mode header {
    background-color: var(--dark-card);
    color: var(--light-text);
  }
  
  h1 .green { color: var(--green); }
  h1 .teal { color: var(--deep-teal); }
  h1 .navy { color: var(--navy); }
  
  #darkModeToggle {
    margin-top: 10px;
    padding: 8px 16px;
    background: var(--navy);
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
  }
  
  main {
    display: flex;
    flex-direction: column;
    gap: 20px;
    padding: 20px;
    max-width: 1000px;
    margin: auto;
  }
  
  .inputs,
  .outputs {
    background: var(--white);
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 4px 10px var(--shadow);
    display: grid;
    gap: 20px;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  }
  
  .dark-mode .inputs,
  .dark-mode .outputs {
    background-color: var(--dark-card);
  }
  
  label {
    display: flex;
    flex-direction: column;
    font-weight: 500;
    font-size: 0.95rem;
  }
  
  input {
    padding: 10px;
    border-radius: 5px;
    border: 1px solid #ccc;
    margin-top: 6px;
    background-color: var(--white);
  }
  
  .dark-mode input {
    background-color: var(--dark-card);
    color: var(--light-text);
    border-color: var(--muted);
  }
  
  #summaryText {
    font-size: 1.2rem;
    font-weight: bold;
    margin-bottom: 10px;
    opacity: 0;
    transition: opacity 0.4s ease;
  }
  
  #summaryText.visible {
    opacity: 1;
  }
  
  #downloadBtn {
    background: var(--green);
    color: white;
    padding: 12px 18px;
    border: none;
    border-radius: 6px;
    font-weight: bold;
    cursor: pointer;
    transition: transform 0.2s ease, background 0.3s ease;
  }
  
  #downloadBtn:hover {
    background: var(--deep-teal);
    transform: scale(1.03);
  }
  
  #downloadBtn:active {
    transform: scale(0.98);
  }
  
  canvas {
    width: 100%;
    max-width: 100%;
    height: 300px;
    border: 1px solid #ccc;
    background-color: #fff;
    border-radius: 8px;
    opacity: 0;
    transition: opacity 0.4s ease;
  }
  
  canvas.visible {
    opacity: 1;
  }
  
  .summary-group {
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    gap: 15px;
  }
  
  footer {
    text-align: center;
    padding: 10px 0 30px;
    font-size: 0.95rem;
    color: var(--muted);
  }
  
  input:focus {
    border-color: var(--green);
    box-shadow: 0 0 5px var(--green);
    outline: none;
  }
  
  @media (max-width: 600px) {
    .inputs,
    .outputs {
      grid-template-columns: 1fr;
    }
  
    canvas {
      height: 250px;
    }
  }
  
  
  /* UX Overlay */
  .overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0,0,0,0.8);
    color: white;
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 999;
  }
  
  .overlay-content {
    background: var(--navy);
    padding: 30px;
    border-radius: 12px;
    text-align: center;
    max-width: 500px;
    box-shadow: 0 4px 10px rgba(0,0,0,0.5);
  }
  
  .overlay-content h2 {
    margin-bottom: 10px;
  }
  
  .overlay-content p {
    font-size: 1rem;
    margin-bottom: 20px;
  }
  
  #startBtn {
    background-color: var(--green);
    color: white;
    padding: 12px 20px;
    border: none;
    border-radius: 6px;
    font-size: 1rem;
    cursor: pointer;
    transition: transform 0.2s ease;
  }
  
  #startBtn:hover {
    transform: scale(1.05);
  }
  
  select {
    padding: 10px;
    border-radius: 5px;
    border: 1px solid #ccc;
    margin-top: 6px;
    background-color: var(--white);
    width: 100%;
  }
  .dark-mode select {
    background-color: var(--dark-card);
    color: var(--light-text);
    border-color: var(--muted);
  }