How to add custom style to meteor accounts ui for react?

Question

I have just started learning react and Meteor. I am using the okgrow:accounts-ui-react to show a login and signup form on my site. You only have to add the component to show the signup/login form on your page. However, the dropdown form is ugly and does not go well with my site's design. Therefore, I want to learn how can you modify the styles of such meteor components. In this case, how can you change the style of this component to appear as a materially design form. I am using materialize.css and I want to know how can I give this login component a materialize design inspired look? I want to make the dropdown inspired by material design and also change the contents of the form. The following is my component that I created by following a video on leveluptuts.

import React, {Component} from 'react';
import { LoginButtons } from 'meteor/okgrow:accounts-ui-react';
class App extends Component{
    render(){
    return (
        <div>
        <header> 
            <h1>Level Up Voting </h1>
            <LoginButtons/>
        </header>
        </div>
        );
    }
}

The following image shows how my login button appears on screen: