:root {
    --teal: #20c997;
    --deep-teal: #138d75;
    --navy: #001f3f;
    --dark-navy: #001737;
    --gray: #f4f4f4;
    --white: #ffffff;
    --muted: #aaa;
    --dark-bg: #1f1f1f;
    --card-dark: #2c2c2c;
    --light-on-dark: #f0f0f0;
  }
  
  * {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
  }
  
  body {
    font-family: 'Segoe UI', sans-serif;
    background-color: var(--gray);
    color: var(--navy);
    transition: background 0.3s, color 0.3s;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
  }
  
  body.dark {
    background-color: var(--dark-bg);
    color: var(--light-on-dark);
  }
  
  /* Header */
  .centered-header {
    text-align: center;
    background: var(--white);
    padding: 2rem 1rem 1.5rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
    position: relative;
  }
  
  body.dark .centered-header {
    background: var(--dark-navy);
  }
  
  .centered-header h1 {
    font-size: 2rem;
    font-weight: bold;
  }
  
  .gradient-text {
    background: linear-gradient(90deg, var(--teal), var(--deep-teal), var(--navy));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    display: inline-block;
  }
  
  #toggle-mode {
    position: absolute;
    top: 1rem;
    right: 1rem;
    font-size: 1.4rem;
    background: none;
    border: none;
    cursor: pointer;
    color: inherit;
  }
  
  /* App Container */
  .app-container {
    background-color: var(--white);
    border-radius: 16px;
    padding: 2rem;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
    transition: background 0.3s;
  }
  
  body.dark .app-container {
    background-color: var(--card-dark);
  }
  
  /* Main Content */
  main {
    flex: 1;
    max-width: 640px;
    margin: auto;
    padding: 1.5rem;
  }
  
  .form-section {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
  }
  
  input {
    padding: 0.75rem;
    border: 1px solid #ccc;
    border-radius: 8px;
    font-size: 1rem;
    background-color: var(--white);
    color: inherit;
  }
  
  body.dark input {
    background-color: var(--card-dark);
    border-color: #444;
    color: var(--light-on-dark);
  }
  
  button {
    padding: 0.75rem;
    border: none;
    border-radius: 8px;
    background: var(--teal);
    color: white;
    font-weight: bold;
    cursor: pointer;
    transition: background 0.3s;
  }
  
  button:hover {
    background: var(--deep-teal);
  }
  
  button.danger {
    background: #dc3545;
  }
  
  button.danger:hover {
    background: #b02a37;
  }
  
  .feedback-message {
    color: #dc3545;
    font-size: 0.9rem;
    display: none;
  }
  
  body.dark .feedback-message {
    color: #ff6b6b;
  }
  
  /* Tabs */
  .tabs-list {
    margin-top: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
  }
  
  .tab-card {
    background: var(--white);
    padding: 0.75rem;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
    display: flex;
    justify-content: space-between;
    align-items: center;
  }
  
  body.dark .tab-card {
    background: var(--card-dark);
  }
  
  .tab-card a {
    color: var(--deep-teal);
    text-decoration: none;
    font-weight: bold;
  }
  
  .tab-card button {
    background: var(--muted);
    color: white;
    font-size: 0.8rem;
    padding: 0.4rem 0.6rem;
    border-radius: 6px;
    border: none;
    margin-left: 0.5rem;
  }
  
  /* Actions & Footer */
  .actions {
    margin-top: 1.5rem;
    text-align: center;
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    justify-content: center;
  }
  
  footer {
    text-align: center;
    padding: 1rem;
    font-size: 0.9rem;
    color: var(--muted);
  }
  
  /* Mobile */
  @media (max-width: 600px) {
    .form-section {
      flex-direction: column;
    }
  
    .centered-header h1 {
      font-size: 1.5rem;
    }
  
    .app-container {
      padding: 1rem;
    }
  }