<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">

<svg width="100px" height="100px" version="1.1"
     xmlns="http://www.w3.org/2000/svg">

<defs>
  <linearGradient id="diagonal" x1="0%" y1="0%" x2="100%" y2="100%">
    <stop offset="0%" style="stop-color:rgb(255,255,0); stop-opacity:1"/>
    <stop offset="100%" style="stop-color:rgb(255,0,0); stop-opacity:1"/>
  </linearGradient>
</defs>

<rect x="10" y="10" width="80" height="80" fill="url(#diagonal)" />

</svg>
