:root {
  color-scheme: light dark;
  background: #ffffff;
  color: #000000;
  font-family: Arial, Helvetica, sans-serif;
}
* { box-sizing: border-box; }
body {
  margin: 0;
  min-height: 100vh;
  min-height: 100svh;
  display: grid;
  place-items: center;
  padding: 16px;
}
main {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
}
.signature-mark {
  display: block;
  width: 80px;
  height: 80px;
}
h1 {
  margin: 0;
  font-size: 18px;
  line-height: 1.25;
  font-weight: 400;
}
@media (max-width: 600px) {
  .signature-mark { width: 72px; height: 72px; }
}
@media (prefers-color-scheme: dark) {
  :root { background: #181818; color: #f5f5f5; }
}