How to style Material UI Tooltip?

How can I style the Material UI Tooltip title? The default tooltip on hover comes out black with no text wrap. Is it possible to change the background, color etc? Is this option even available?

The other popular answer (by André Junges) on this question is for the 0.x versions of Material-UI. Below I've copied in my answer from Material UI's Tooltip - Customization Style which addresses this for v3 and v4. Further down, I have added a version of the example using v5.

Below are examples of how to override all tooltips via the theme, or to just customize a single tooltip using withStyles (two different examples). The second approach could also be used to create a custom tooltip component that you could reuse without forcing it to be used globally.

import React from "react";
import ReactDOM from "react-dom";

import {
  createMuiTheme,
  MuiThemeProvider,
  withStyles
} from "@material-ui/core/styles";
import Tooltip from "@material-ui/core/Tooltip";

const defaultTheme = createMuiTheme();
const theme = createMuiTheme({
  overrides: {
    MuiTooltip: {
      tooltip: {
        fontSize: "2em",
        color: "yellow",
        backgroundColor: "red"
      }
    }
  }
});
const BlueOnGreenTooltip = withStyles({
  tooltip: {
    color: "lightblue",
    backgroundColor: "green"
  }
})(Tooltip);

const TextOnlyTooltip = withStyles({
  tooltip: {
    color: "black",
    backgroundColor: "transparent"
  }
})(Tooltip);

function App(props) {
  return (
    <MuiThemeProvider theme={defaultTheme}>
      <div className="App">
        <MuiThemeProvider theme={theme}>
          <Tooltip title="This tooltip is customized via overrides in the theme">
            <div style={{ marginBottom: "20px" }}>
              Hover to see tooltip customized via theme
            </div>
          </Tooltip>
        </MuiThemeProvider>
        <BlueOnGreenTooltip title="This tooltip is customized via withStyles">
          <div style={{ marginBottom: "20px" }}>
            Hover to see blue-on-green tooltip customized via withStyles
          </div>
        </BlueOnGreenTooltip>
        <TextOnlyTooltip title="This tooltip is customized via withStyles">
          <div>Hover to see text-only tooltip customized via withStyles</div>
        </TextOnlyTooltip>
      </div>
    </MuiThemeProvider>
  );
}
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

Here is documentation on tooltip CSS classes available to control different aspects of tooltip behavior: https://material-ui.com/api/tooltip/#css

Here is documentation on overriding these classes in the theme: https://material-ui.com/customization/components/#global-theme-override

Here is a similar example, but updated to work with v5 of Material-UI (pay attention that it works in 5.0.3 and upper versions after some fixes). It includes customization via the theme, customization using styled, and customization using the sx prop. All of these customizations target the "tooltip slot" so that the CSS is applied to the element that controls the visual look of the tooltip.

import React from "react";
import ReactDOM from "react-dom";

import { createTheme, ThemeProvider, styled } from "@mui/material/styles";
import Tooltip from "@mui/material/Tooltip";

const defaultTheme = createTheme();
const theme = createTheme({
  components: {
    MuiTooltip: {
      styleOverrides: {
        tooltip: {
          fontSize: "2em",
          color: "yellow",
          backgroundColor: "red"
        }
      }
    }
  }
});
const BlueOnGreenTooltip = styled(({ className, ...props }) => (
  <Tooltip {...props} componentsProps={{ tooltip: { className: className } }} />
))(`
    color: lightblue;
    background-color: green;
    font-size: 1.5em;
`);

const TextOnlyTooltip = styled(({ className, ...props }) => (
  <Tooltip {...props} componentsProps={{ tooltip: { className: className } }} />
))(`
    color: black;
    background-color: transparent;
`);

function App(props) {
  return (
    <ThemeProvider theme={defaultTheme}>
      <div className="App">
        <ThemeProvider theme={theme}>
          <Tooltip title="This tooltip is customized via overrides in the theme">
            <div style={{ marginBottom: "20px" }}>
              Hover to see tooltip customized via theme
            </div>
          </Tooltip>
        </ThemeProvider>
        <BlueOnGreenTooltip title="This tooltip is customized via styled">
          <div style={{ marginBottom: "20px" }}>
            Hover to see blue-on-green tooltip customized via styled
          </div>
        </BlueOnGreenTooltip>
        <TextOnlyTooltip title="This tooltip is customized via styled">
          <div style={{ marginBottom: "20px" }}>
            Hover to see text-only tooltip customized via styled
          </div>
        </TextOnlyTooltip>
        <Tooltip
          title="This tooltip is customized via the sx prop"
          componentsProps={{
            tooltip: {
              sx: {
                color: "purple",
                backgroundColor: "lightblue",
                fontSize: "2em"
              }
            }
          }}
        >
          <div>
            Hover to see purple-on-blue tooltip customized via the sx prop
          </div>
        </Tooltip>
      </div>
    </ThemeProvider>
  );
}
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

Documentation on changes to the theme structure between v4 and v5: https://mui.com/guides/migration-v4/#theme

Tooltip customization examples in the Material-UI documentation: https://mui.com/components/tooltips/#customization