Pretty much vanilla, but it depends on the component.
For components that need reactivity and have frequent renders, I use lit-html for rendering on a property setter change.
I mix and match components from different frameworks, I use vaadin-router, but sometimes include lightweight components from other systems too (ionic, shoelace, mwc, etc...).
Mostly though, it's just light-dom vanilla Web components with bootstrap (or similar) for base styles.
For components that need reactivity and have frequent renders, I use lit-html for rendering on a property setter change.
I mix and match components from different frameworks, I use vaadin-router, but sometimes include lightweight components from other systems too (ionic, shoelace, mwc, etc...).
Mostly though, it's just light-dom vanilla Web components with bootstrap (or similar) for base styles.