.modal-heading{
background-color: #038F43;
height: 30px;
color: #fff;
margin: 5px 0px 10px 0px;
}
.nav-tabs .nav-link{
background-color: #0d1323;
border: 1px solid #0d1323;
color: #fff;
font-size: 12px;
}
.nav-tabs .nav-link:hover{
background-color: gray;
}

.nav-tabs .nav-link.active{
background-color: #038F43 !important;
color: #fff !important;
font-size: 12px;
}
.nav-tabs .nav-link.active:hover{
background-color: gray;
}



and Small change in .Ts File,Add encapsulation: ViewEncapsulation.None

import { Component, OnInit, ViewEncapsulation } from '@angular/core';
import { BsModalService, BsModalRef } from 'ngx-bootstrap/modal';

@Component({
  selector: 'app-add-edit-golf-league-manager',
  templateUrl: './add-edit-golf-league-manager.component.html',
  styleUrls: ['./add-edit-golf-league-manager.component.css'],
  encapsulation: ViewEncapsulation.None
  })