As for Angular 5 to change the class of one component from another?

Hi all.
Let's say I have a navbar component.component.ts with html
Navigation

And there is a second component aside.component.ts

By clicking the button in the component aside you are going to change the class navbar component, for example : class test class test1. These components are neither children nor parent each other.
Code optional, just tell me which way to look.
Thank you.