FilledAlerts.tsx

import React from 'react';
import { makeStyles, Theme, createStyles } from '@material-ui/core/styles';
import { Alert } from '@material-ui/lab';

const useStyles = makeStyles((theme: Theme) =>
  createStyles({
    root: {
      width: '100%',
      '& > * + *': {
        marginTop: theme.spacing(2),
      },
    },
  }),
);

export default function SimpleAlerts() {
  const classes = useStyles();

  return (
    <div className={classes.root}>
      <Alert variant="filled" severity="error">
        This is an error alert—check it out!
      </Alert>
      <Alert variant="filled" severity="warning">
        This is a warning alert—check it out!
      </Alert>
      <Alert variant="filled" severity="info">
        This is an info alert—check it out!
      </Alert>
      <Alert variant="filled" severity="success">
        This is a success alert—check it out!
      </Alert>
    </div>
  );
}