问在angular中更改特定页面上的导航栏背景颜色

EN

    import { Component, OnInit } from '@angular/core';

    @Component({
      selector   : 'app-navbar',
      templateUrl: './navbar.component.html',
      styleUrls  : ['./navbar.component.scss'],
      // template: '<img src="assets/img/wr-logo.png">'
      template: `
      <nav class="navbar navbar-expand-md navbar-fixed-top navbar-light bg-white main-nav" id="navbar navbar-change">
        <div class="container">
            <div class="navbar-collapse-nil collapse-nil nav-content order-1">
                <ul class="nav navbar-nav">
                    <li class="nav-item active">
                        <a class="nav-link" routerLink="/home/" id="imagelogo"></a>
                    </li>

                </ul>
            </div>
            <ul class="nav navbar-nav text-nowrap flex-row mx-md-auto order-2 order-md-2" id="center-nav-item">
            <div id="hoverDrop">
            <div class="dropdown">
            <button class="dropbtn">{{product_nav}}</button>
            <div class="dropdown-content">
              <a routerLink="/hours-of-rest/">{{hor_nav}}</a>
              <a routerLink="/on-leave/">{{leave_nav}}</a>

            </div>
          </div>
            </div>


              <li class="nav-item">
                <a class="nav-link" routerLink="/tour/">{{tour_nav}}</a>
              </li>
              <li class="nav-item">
                <a class="nav-link" routerLink="/pricing/">{{pricing_nav}}</a>
              </li>
              <li class="nav-item">
                <a class="nav-link" routerLink="/resources/">{{resources_nav}}</a>
              </li>

            </ul>
            <div class="ml-auto navbar-collapse-nil collapse-nil nav-content order-3 order-md-3" id="right-nav-item">
                <ul class="ml-auto nav navbar-nav">
                  <li class="nav-item"  onclick="blueNav">
                    <a class="nav-link" routerLink="/contact/" id="contact-nav-element" routerLinkActive="blue-active-link" [routerLinkActiveOptions]="{exact:
                      true}">{{contact_nav}}</a>
                  </li>

                  <li class="nav-item">
                    <a class="nav-link" href="https://google.com/" id="login-nav-element">{{login_nav}}  <i class="fa fa-arrow-right" aria-hidden="true"></i></a>
                  </li>
                </ul>
            </div>
        </div>
      </nav>
      `
    })
    export class NavbarComponent implements OnInit {

      product_nav:string;
      hor_nav:string;
      leave_nav:string;
      tour_nav:string;
      pricing_nav:string;
      resources_nav:string;
      contact_nav:string;
      login_nav:string;

      constructor() {

      }

      ngOnInit() {

        this.product_nav = 'Product';
        this.hor_nav = 'HoR';
        this.leave_nav = 'Leave';
        this.tour_nav = 'Tour';
        this.pricing_nav = 'Pricing';
        this.resources_nav = 'Resources';
        this.contact_nav = 'Contact';
        this.login_nav = 'Login';

        /* When the user scrolls down, hide the navbar. When the user scrolls up, show the navbar */
      var prevScrollpos = window.pageYOffset;
      window.onscroll = function() {
        var currentScrollPos = window.pageYOffset;
        if (prevScrollpos > currentScrollPos) {
          document.getElementById("navbar").style.top = "0";
        } else {
          document.getElementById("navbar").style.top = "-50px";
        }
        prevScrollpos = currentScrollPos;
      }




// window.onclick =
  //    function blueNav(){
  //    var blueTop = document.getElementByTagName("navbar");
  //      var i;
  //      for (i = 0; i < blueTop.length; i++) {
  //          blueTop[i].style.backgroundColor = "blue";
  //      }
  //    }


      window.onclick =
      function blueNav(){
        var blueTop = document.getElementById("navbar");
        var i;
        for (i = 0; i < blueTop.length; i++) {
            blueTop[i].style.backgroundColor = "blue";
        }
      }

      }

    }