<svg width="10cm" height="5cm" viewBox="0 0 1000 500" version="1.1">
     <defs>
          <style type="text/css"> rect { fill: red; stroke: blue; stroke-width: 3 } </style>
     </defs>
     <rect x="200" y="100" width="600" height="300"/>
</svg>
Original SVG source