how to give a svg a circle look code example

Example 1: svg circle

<svg width="100" height="100">
  <circle cx="50%" cy="50%" r="10" fill="red"/>
</svg>

Example 2: svg circle

<svg viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
  <circle cx="50" cy="50" r="50"/>
</svg>