developing responsive pages has nothing to do with vue, vue is just a js framework. Response is mainly css and html, how do you usually develop, or the same development.

flex layout itself mainly solves the layout problem, because flex can well control self-growing elements and fixed-size elements, so it partially achieves the purpose of responsiveness. If you need more responsive control, you still need to use media query.

rem works well.

rem elastic layout or media query