Despite operating in a reduced capacity, the US cybersecurity agency CISA has issued a warning about ongoing attacks exploiting vulnerabilities in Chrome, Zimbra, ThreatSonar, and an ActiveX module.
Base itself is a pretty thin CSS framework built on top of Normalize CSS. Include what you need on top of Base such as custom typography, custom grids, components and make it yours.
Preview all supported themes. Test every feature of each existing control and check source code directly in the app to learn how to implement it. Check color palette and modify theme color contrast.