<svg xmlns="http://www.w3.org/2000/svg"
     xmlns:xlink="http://www.w3.org/1999/xlink"
>
  <style>
    rect { fill: blue !important; }
  </style>
  <rect x="15" y="15" width="200" height="200">
    <set attributeName="fill" attributeType="CSS"
         to="red" begin="0s" fill="freeze"/>
  </rect>
</svg>