How to pass styles to child component and use it as scoped style in Vue?

If you want to target the child elements with scoped styling you have to use the deep selector.

Which can be done with

a >>> b { color : red; }
/deep/ a b { color : red; }
a::v-deep b { color : red; }

Here is the full explanation: https://vue-loader.vuejs.org/guide/scoped-css.html#child-component-root-elements