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                <div class="wrapper" >
      <circle cx="50%" cy="50%" r="35.355%" fill="blueviolet" />
      <rect x="25%" y="25%" width="50%" height="50%" fill="navy" />
  Demonstration of percentage lengths in SVG.  Horizontal percentages are relative to width, vertical percentages are relative to height, but lengths without a clear direction, such as circle radius or font size, are calculated using a geometric average.  Which preserves the Pythagorean relationship of diagonal lines to rectangular lines, but is otherwise somewhat confusing.
  Resize the container above (or the window if you're stuck in a browser that doesn't support CSS resize) to see the effect of changing height and width.  The corners of the rectangle will always just touch the edge of the circle, regardless of the SVG dimensions; but the circle itself may sometimes be too large to fit in the SVG.
  P.S.  <code>35.355% = sqrt(50%)/2</code>


                .wrapper {
    height: 15vh;
    width: 20vw;
    resize: both;
    overflow: scroll;
    border: solid gray;
    margin: 1em;
    position: relative;
svg {
    position: absolute;
    display: block;
    height: 100%;
    width: 100%;
    background: #ccf;