react-test/docs/data/joy/components/table/TableColumnWidth.js

import Table from '@mui/joy/Table';

function createData(name, calories, fat, carbs, protein) {
  return { name, calories, fat, carbs, protein };
}

const rows = [
  createData('Frozen yoghurt', 159, 6.0, 24, 4.0),
  createData('Ice cream sandwich', 237, 9.0, 37, 4.3),
  createData('Eclair', 262, 16.0, 24, 6.0),
  createData('Cupcake', 305, 3.7, 67, 4.3),
  createData('Gingerbread', 356, 16.0, 49, 3.9),
];

export default function TableColumnWidth() {
  return (
    <Table sx={{ '& thead th:nth-child(1)': { width: '40%' } }}>
      <thead>
        <tr>
          <th>Column width (40%)</th>
          <th>Calories</th>
          <th>Fat&nbsp;(g)</th>
          <th>Carbs&nbsp;(g)</th>
          <th>Protein&nbsp;(g)</th>
        </tr>
      </thead>
      <tbody>
        {rows.map((row) => (
          <tr key={row.name}>
            <td>{row.name}</td>
            <td>{row.calories}</td>
            <td>{row.fat}</td>
            <td>{row.carbs}</td>
            <td>{row.protein}</td>
          </tr>
        ))}
      </tbody>
    </Table>
  );
}