Step-3 Style component

App.js

import React, { Component } from 'react';
import styled from 'styled-components';

const mainColor = 'indianred'

const Title = styled.h1`
  color: ${props => props.color ||  'goldenrod'};
  font-size: 2.8em;
  margin: 25px;
  padding-bottom: 20px;
  border-bottom: 1px solid ${mainColor};
  display: inline-block;
`;

class App extends Component {
  render() {
    return (
      <div className={this.props.className}>
        <Title color={mainColor}>Mystagram</Title>
      </div>
    );
  }
}

export default styled(App)`
  width: 100vw;
  height: 100vh;
  text-align: center;
`;