If that was designed from the ground up, have you considered a library with ready to use components and if yes, can you share the reason for the current approach? I personally like the styling of Tailwind.
I know there are pros and cons with everything, but a library would possibly give you responsive layout out of the box, consistent styling, fonts, paddings, etc. For a small dev team and large site that might be the easier solution. Displaying large sets of data and forms on a site is one of the hardest things to design.
As for the fonts, Verdana and Ariel are really outdated for the web, they must only be used as fallbacks. There are many modern web fonts that are much nicer, I personally used Rubik for my site, but a typical font-family definition looks like this:
"Rubik", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif
where "Rubik" is my embedded web font.
It depends whether you want the same font on all devices or not. Other popular web fonts are Lato, Montserrat, Roboto, Noto Sans, Open Sans. You also need to account for localization, but I don't think that is a feature you're going to support.
PS: I don't know what jquery is still used for, but the versoin is really old (from 2012).
PS2:
I feel few things are better, but overall there's no consistency and the perception is not that good - perhaps there aren't many common components and layouts and everything is done per page basis, which would be a nightmare to fix and support. There are also many UX issues, e.g. like tags/pills looking exactly the same as buttons, no loading indicators (page simply jumps when a container gets its data replaced), non-clickable elements like dropdown list items (you need to click on the text), inconsistent pointer style (cursor).