<svg xmlns="http://www.w3.org/2000/svg" width="640" height="640" viewBox="0 0 640 640" role="img" aria-label="dark_square placeholder">
  <defs>
    <linearGradient id="bg" x1="0" y1="0" x2="1" y2="1">
      <stop offset="0%" stop-color="#0f172a"/>
      <stop offset="100%" stop-color="#020617"/>
    </linearGradient>
    <pattern id="grid" width="40" height="40" patternUnits="userSpaceOnUse">
      <path d="M 40 0 L 0 0 0 40" fill="none" stroke="#334155" stroke-width="1" opacity="0.35"/>
    </pattern>
  </defs>
  <rect width="100%" height="100%" fill="url(#bg)"/>
  <rect width="100%" height="100%" fill="url(#grid)"/>
  <rect x="12" y="12" width="616" height="616" fill="none" stroke="#64748b" stroke-width="6" stroke-dasharray="20 12" opacity="0.9"/>
  <rect x="12" y="129" width="616" height="381" rx="16" fill="#0f172a" opacity="0.88" stroke="#94a3b8" stroke-width="4"/>
  <text x="320" y="320" text-anchor="middle" dominant-baseline="middle" font-family="ui-sans-serif, system-ui, Segoe UI, Roboto, Arial, sans-serif" fill="#f8fafc">
    <tspan x="320" dy="-92" font-size="77px" font-weight="700">640 × 640</tspan>
    <tspan x="320" dy="92" font-size="60px" font-weight="600" fill="#e2e8f0">Aspect ratio 1:1</tspan>
    <tspan x="320" dy="92" font-size="60px" font-weight="500" fill="#cbd5e1">dark_square</tspan>
  </text>
</svg>