UPDATE: uhm, this seems working for me in landscape and portrait mode:
Code:
<p style="text-align:center"><svg width="100%" height="100%" preserveAspectRatio="xMidYMid meet" viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg" version="1.1" xmlns:xlink="http://www.w3.org/1999/xlink">
<circle cx="50" cy="50" r="40" stroke="black" stroke-width="3" fill="red" />
</svg>
</p>