SVG P3 gradient

HTML

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 300 350">
  <linearGradient id="Gradient-0" x1="0" y1="11.5" x2="166" y2="11.5" gradientUnits="userSpaceOnUse">
    <stop offset="0" stop-color="rgb(255, 0, 0)"/>
    <stop offset="0.5" stop-color="color(display-p3 1 0 0)"/>
    <stop offset="1" stop-color="rgb(255, 0, 0)"/>
  </linearGradient>
  <rect x="10" y="10" width="166" height="30" fill="url(#Gradient-0)"/>

  <rect x="50" y="95" width="70" height="70" style="fill: rgb(255, 0, 0)"/>
  <rect x="160" y="95" width="70" height="70" style="fill: color(display-p3 1 0 0)"/>

</svg>