ng zorro icon color changed problem after following official documentation

Question

I'm using ng zorro with angular. and i want to change the icon color of ng zorro, i followed official documentation but icon can be color with span tag only but i'm not using span tag. here is my code:

  <li>
    <ul>
      <li>
        <a>Welcome</a>
      </li>
      <li>
        <a>Monitor</a>
      </li>
      <li>
        <a>Workplace</a>
      </li>
    </ul>
  </li>

i want to be my icon colored