Ask HN: Is there a simple web UI toolbox for back-end devs?

Slack has, for example, the Bolt frameworks (https://api.slack.com/tools/bolt) where a back-end developer can leverage the Slack UI to build whole apps. It is possible to build quite complex workflows without leaving the back-end language of the framework, using Slack Block Kit (https://api.slack.com/block-kit) like lego pieces of a simple UI.

Is there something else similar, a framework/platform where one (mainly a back-end dev) can build an app using ready UI components?