SVG 占位图生成器

<svg xmlns="http://www.w3.org/2000/svg" width="600" height="400" viewBox="0 0 600 400"><rect width="100%" height="100%" fill="#cccccc"/><text x="50%" y="50%" font-family="sans-serif" font-size="50" fill="#666666" text-anchor="middle" dominant-baseline="middle">600×400</text></svg>

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