How to apply custom animation effect @keyframes in MaterialUI using makestyles()

Here is an example demonstrating the keyframes syntax within makeStyles:

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

import { makeStyles } from "@material-ui/core/styles";
import Button from "@material-ui/core/Button";
import clsx from "clsx";

const useStyles = makeStyles(theme => ({
  animatedItem: {
    animation: `$myEffect 3000ms ${theme.transitions.easing.easeInOut}`
  },
  animatedItemExiting: {
    animation: `$myEffectExit 3000ms ${theme.transitions.easing.easeInOut}`,
    opacity: 0,
    transform: "translateY(-200%)"
  },
  "@keyframes myEffect": {
    "0%": {
      opacity: 0,
      transform: "translateY(-200%)"
    },
    "100%": {
      opacity: 1,
      transform: "translateY(0)"
    }
  },
  "@keyframes myEffectExit": {
    "0%": {
      opacity: 1,
      transform: "translateY(0)"
    },
    "100%": {
      opacity: 0,
      transform: "translateY(-200%)"
    }
  }
}));

function App() {
  const classes = useStyles();
  const [exit, setExit] = React.useState(false);
  return (
    <>
      <div
        className={clsx(classes.animatedItem, {
          [classes.animatedItemExiting]: exit
        })}
      >
        <h1>Hello CodeSandbox</h1>
        <h2>Start editing to see some magic happen!</h2>
        <Button onClick={() => setExit(true)}>Click to exit</Button>
      </div>
      {exit && <Button onClick={() => setExit(false)}>Click to enter</Button>}
    </>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

Documentation: https://cssinjs.org/jss-syntax/?v=v10.0.0#keyframes-animation

Just some notes on top of @Ryan's answer. If you define the keyframe using makeStyles. Remember to prefix the animation name with $. I missed this small detail the first time and my code didn't work, in the example below

const useStyles = makeStyles({
  "@keyframes fadeIn": {
    "0%": {
      opacity: 0,
      transform: "translateY(5rem)"
    },
    "100%": {
      opacity: 1,
      transform: "translateY(0)"
    }
  },
  selector: {
    animation: "$fadeIn .2s ease-in-out"
  }
});

Instead of

animation: "fadeIn .2s ease-in-out"

It should be

animation: "$fadeIn .2s ease-in-out"

But if you define the keyframe in global scope. The prefix is unnecessary here

const useStyles = makeStyles({
  "@global": {
    "@keyframes fadeIn": {
      "0%": {
        opacity: 0,
        transform: "translateY(5rem)"
      },
      "100%": {
        opacity: 1,
        transform: "translateY(0)"
      }
    }
  },
  selector: {
    animation: "fadeIn .2s ease-in-out" // --> this works
  }
});

Follow this issue on github for more discussion about this.