PROBLEM 1 :-
when router-outlet is included in app.component.html with other html elements like div,paragraph etc.
After running the site i saw,the output is blank.
when i run ng serve in command prompt.
for eg:- app.component.html
<div style='text-align:center'>
<h1>
welcome to Technology
<h1>
<h2>hello angular6'<h2>'
<div>
SOLUTION:-
ADD CUSTOM_ELEMENTS_SCHEMA IN APP.MODULE.TS
import { NgModule,CUSTOM_ELEMENTS_SCHEMA } from @angular/core;
@NgModule({
schemas: [CUSTOM_ELEMENTS_SCHEMA],
declarations: [
AppComponent
],
NOW WHEN YOU RUN NG SERVE,YOU CAN SEE THE APP.COMPONENT.HTML with full DESIGN.