It is important to change the style precedence order with the help of the
StyledEngineProvider
component, otherwise the internal MUI classes will overwrite
your styles.
@react.component
let make = () =>
<Mui.StyledEngineProvider injectFirst=true>
<Mui.Button
color=#primary
className="my-global-class-name"
onClick=ignore>
{React.string("Hello, plain CSS & MUI!")}
</Mui.Button>
</Mui.StyledEngineProvider>