Answer by Jeff McCloud for Material-ui horizontal menu

Set the CSS className on the Menu that styles its immediate DIV children with "display: inline-block"

Working jsFiddle: https://jsfiddle.net/d980vcon/2/

in CSS:

.horiz-menu > div {  display: inline-block;}

In JSX:

class Example extends React.Component {  render() {    return (<Menu className="horiz-menu"><MenuItem primaryText="Home"/><MenuItem primaryText="Test Menu 1" /><MenuItem primaryText="Test Menu 2" /><MenuItem primaryText="About" /></Menu>    );  }}