mastodon/app/assets/javascripts/components/components/button.jsx

const Button = React.createClass({
  propTypes: {
    text: React.PropTypes.string.isRequired,
    onClick: React.PropTypes.func
  },

  handleClick (e) {
    e.preventDefault();
    this.props.onClick();
  },

  render () {
    return (
      <a href='#' onClick={this.handleClick} style={{ display: 'inline-block', position: 'relative', boxSizing: 'border-box', textAlign: 'center', border: '10px none', backgroundColor: '#2b90d9', color: '#fff', fontSize: '14px', fontWeight: '500', letterSpacing: '0', textTransform: 'uppercase', padding: '0 16px', height: '36px', cursor: 'pointer', lineHeight: '36px', borderRadius: '4px', textDecoration: 'none' }}>
        {this.props.text}
      </a>
    );
  }

});

export default Button;