You want the smallest, simplest svg's possbile

See tutorial at :

https://developer.mozilla.org/en-US/docs/Web/SVG/Tutorial/Getting_Started






See and example at :

  https://developer.mozilla.org/en-US/docs/Web/SVG/Element/defs


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<svg width="80px" height="30px" viewBox="0 0 80 30"
     xmlns="http://www.w3.org/2000/svg">

  <defs>
    <linearGradient id="Gradient01">
      <stop offset="20%" stop-color="#39F" />
      <stop offset="90%" stop-color="#F3F" />
    </linearGradient>
  </defs>

  <rect x="10" y="10" width="60" height="10" 
        fill="url(#Gradient01)" />
</svg>

* *****************************************************