Contact form with dark mode

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <title>Contact us</title>
    <style>
      :root {
        --page: #f4f4f5;
        --surface: #ffffff;
        --text: #18181b;
        --muted: #71717a;
        --line: #e4e4e7;
        --input-line: #d4d4d8;
        --accent: #18181b;
        --accent-text: #ffffff;
      }
      @media (prefers-color-scheme: dark) {
        :root {
          --page: #09090b;
          --surface: #18181b;
          --text: #fafafa;
          --muted: #a1a1aa;
          --line: #27272a;
          --input-line: #3f3f46;
          --accent: #fafafa;
          --accent-text: #18181b;
        }
      }
      *, *::before, *::after { box-sizing: border-box; }
      body {
        margin: 0;
        padding: 32px 16px;
        font-family: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
        background: var(--page);
        color: var(--text);
      }
      .card {
        max-width: 460px;
        margin: 0 auto;
        padding: 28px;
        background: var(--surface);
        border: 1px solid var(--line);
        border-radius: 12px;
      }
      h1 { margin: 0 0 6px; font-size: 20px; }
      .sub { margin: 0 0 22px; font-size: 14px; color: var(--muted); }
      .field { margin-bottom: 16px; }
      label { display: block; margin-bottom: 6px; font-size: 13px; font-weight: 500; }
      input, textarea {
        width: 100%;
        padding: 10px 12px;
        font: inherit;
        font-size: 14px;
        color: var(--text);
        background: var(--surface);
        border: 1px solid var(--input-line);
        border-radius: 8px;
      }
      input:focus, textarea:focus {
        outline: 2px solid var(--accent);
        outline-offset: 1px;
        border-color: transparent;
      }
      textarea { min-height: 110px; resize: vertical; }
      button {
        width: 100%;
        padding: 11px 16px;
        font: inherit;
        font-size: 14px;
        font-weight: 500;
        color: var(--accent-text);
        background: var(--accent);
        border: 0;
        border-radius: 8px;
        cursor: pointer;
      }
      button:active { transform: scale(0.99); }
      .hp { display: none; }
    </style>
  </head>
  <body>
    <form class="card" action="https://app.portform.co/api/submit" method="POST">
      <h1>Get in touch</h1>
      <p class="sub">This form follows your system theme.</p>

      <input type="hidden" name="access_key" value="YOUR_ACCESS_KEY" />
      <input type="checkbox" name="botcheck" class="hp" tabindex="-1" autocomplete="off" />

      <div class="field">
        <label for="name">Name</label>
        <input id="name" type="text" name="name" autocomplete="name" required />
      </div>
      <div class="field">
        <label for="email">Email</label>
        <input id="email" type="email" name="email" autocomplete="email" required />
      </div>
      <div class="field">
        <label for="message">Message</label>
        <textarea id="message" name="message" required></textarea>
      </div>

      <button type="submit">Send message</button>
    </form>
  </body>
</html>