<!DOCTYPE html>
<div style="outline: dashed lightblue; height: 300px; width: 400px;">
    <svg style="background-color: yellow; max-width: 100%; max-height: 100%;" width="100%" viewBox="0 0 900 300">
        <rect x="0" y="0" width="900" height="300" />
    </svg>
</div>