<defs>
<linearGradient
id="rougeBleu"
x1="0%" y1="0%" x2="100%" y2="0%">
<stop
offset="0%"
stop-color="crimson"
stop-opacity="1" />
<stop
offset="100%"
stop-color="deepSkyBlue"
stop-opacity="1" />
</linearGradient>
</defs>
<circle cx="64" cy="64" r="40" fill="url(#rougeBleu)"/>