materialuiupgraded/packages/material-ui/src/styles/zIndex.js

Material-UI's workspace package

// We need to centralize the zIndex definitions as they work
// like global values in the browser.
const zIndex = {
  mobileStepper: 1000,
  appBar: 1100,
  drawer: 1200,
  modal: 1300,
  snackbar: 1400,
  tooltip: 1500,
};

export default zIndex;