tootlab-mastodon/app/javascript/mastodon/components/avatar_overlay.js

import React from 'react';
import PropTypes from 'prop-types';

class AvatarOverlay extends React.PureComponent {
  static propTypes = {
    staticSrc: PropTypes.string.isRequired,
    overlaySrc: PropTypes.string.isRequired
  };

  render() {
    const {staticSrc, overlaySrc} = this.props;

    const baseStyle = {
      backgroundImage: `url(${staticSrc})`
    };

    const overlayStyle = {
      backgroundImage: `url(${overlaySrc})`
    };

    return (
      <div className='account__avatar-overlay'>
        <div className="account__avatar-overlay-base" style={baseStyle} />
        <div className="account__avatar-overlay-overlay" style={overlayStyle} />
      </div>
    );
  }

}

export default AvatarOverlay;