Well you can do that in calibre as well without needing SVG by using the canvas element. Something like this for a header template
Code:
<header><canvas><script>
canvas = document.currentScript.parentNode
canvas.height = canvas.parentNode.scrollHeight
canvas.width = 1400
ctx = canvas.getContext("2d");
ctx.font = (canvas.parentNode.scrollHeight / 2) + "px sans-serif"
ctx.fillStyle = 'yellow';
ctx.fillRect(0, 0, canvas.width, canvas.height)
ctx.fillStyle = 'black';
ctx.fillText("section: _SECTION_", 5, canvas.parentNode.scrollHeight / 2);
You will need to edit the various sizes to get it to work well for your conversion.