Not without custom CSS, and that requires itch.io to enable CSS support on the account.
With the code listings on this page, it seems like there's something wrong with the CR/Line feeds.
I just did a quick test on a test page here on Itch with code from the ULAplus spec and it shows up normal when creating a code-block.
The only thing that Itch does is remove "empty" lines (ie before the "header:", "basic:" labels, etc.) but that can be easily fixed by putting only a space on those lines.
