<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64">
  <style>
    rect { fill: #111113; }
    text { fill: #fbfbfb; }
    @media (prefers-color-scheme: dark) {
      rect { fill: #ededef; }
      text { fill: #0b0b0c; }
    }
  </style>
  <rect width="64" height="64" rx="15"/>
  <text x="32" y="46" text-anchor="middle" font-family="ui-sans-serif, system-ui, sans-serif" font-size="42" font-weight="600" letter-spacing="-2">a</text>
</svg>
