custom directive - Angular 2/4/5

currently using angular 5 cli. i don't know why my custom directive not working. and not even showing error in my console. am trying to some style to maintain full image width.

so far.

import { Directive,ElementRef,Renderer } from '@angular/core';

@Directive({
  selector: '[fullWidthImg]'
})
export class MyStyleDirective {

  constructor(private el: ElementRef, private renderer:Renderer){
    renderer.setElementStyle(el.nativeElement,'background-image', 'url("https://mdbootstrap.com/img/Photos/Horizontal/Nature/full page/img(20).jpg")')
    renderer.setElementStyle(el.nativeElement,'height', '100%")')
    renderer.setElementStyle(el.nativeElement,'background-position', 'center')
    renderer.setElementStyle(el.nativeElement,'background-repeat', 'no-repeat')
    renderer.setElementStyle(el.nativeElement,' background-size','cover')
  }

}

copied from other resource

import { Directive, ElementRef, AfterViewInit } from '@angular/core';

@Directive({ 
     selector: '[fullWidthImg]' 
})
export class MyStyleDirective implements AfterViewInit {
    constructor(private elRef: ElementRef) {
    }
    ngAfterViewInit(): void {
       this.elRef.nativeElement.style.backgroundImage = 'url("https://mdbootstrap.com/img/Photos/Horizontal/Nature/full page/img(20).jpg")';
       //this.elRef.nativeElement.style.fontSize = '20px';
    }       
} 

html

<div fullWidthImg></div>

where am doing wrong. if possible pls provide live example or good resource to understand custom directive

thank you

Try this One:

<div fullWidthImg [ngStyle]="{'height': '200px', 'width':'200px'}"> </div>

Rest of code is working just change div tag only!! Here is working example : Image display