Ask HN: How to make bootstrap look more professional

I'm developing an application for use by the internal users of a public sector organization. There aren't any requirements for fancy UI so I'm just using good old bootstrap 4. However, I think that the defaults don't look as much professional, or if you want "enterpris-y". Could you recommend me a better approach? Ideally I'd like to just keep my bootstrap layout and change some fonts / colors / sizes etc by an extra css style that would override the bootstrap 4 defaults.

Thank you!