Because the overflow is hidden and the vertical alignment is middle, I’m guessing it’s hidden behind the form elements (which probably have a 100% width as well…).
Highlight the markup in the developer tools, and it should highlight the element itself, even if it’s hidden behind something else…
Is this just for a background or does it have some other purpose? If its a background then it should be a background svg instead (assuming you want content on top) or indeed a linear gradient would do the trick.
That’s part of the bootstrap default min.css files so I doubt that will be the issue here. As you say it may be hidden behind something else or indeed the parent element may have a width and height of zero or any number of other things.
The parent element definitely has a play here… if you spot the box model in the second screenshot, the SVG is identifying itself as being 442x100, which… unless you’ve got a REALLY low resolution on your monitor…