How to apply CSS in Structural Directive?

I was making my own directive Structure Directive what I want is when the value is present in the UI part then this will be telling my directive that i have the value now so make is beautiful with CSS ( with the help of viewContainerRef from @angular/core )

1. what I want is whenever the value is present How to apply CSS on Structural Directive ?

Here is my code

HTML Part

<p *myDirective="type">{{err}}</p> 

myDirective as Directive Class

Any help would Appreciate.