How to apply custom animation effect @keyframes in MUI?

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

---

For those who have started using Material-UI v5 and want to know how to do this using Emotion rather than makeStyles, below is an example of one way to do the equivalent styles using Emotion.

/** @jsxImportSource @emotion/react */
import React from "react";
import ReactDOM from "react-dom";

import { css, keyframes } from "@emotion/react";
import { useTheme } from "@mui/material/styles";
import Button from "@mui/material/Button";

const myEffect = keyframes`
  0% {
    opacity: 0;
    transform: translateY(-200%);
  }
  100% {
    opacity: 1;
    transform: translateY(0);
  }
`;
const myEffectExit = keyframes`
  0% {
    opacity: 1;
    transform: translateY(0);
  }
  100% {
    opacity: 0;
    transform: translateY(-200%);
  }
`;

function App() {
  const theme = useTheme();
  const animatedItem = css`
    animation: ${myEffect} 3000ms ${theme.transitions.easing.easeInOut};
  `;
  const animatedItemExiting = css`
    animation: ${myEffectExit} 3000ms ${theme.transitions.easing.easeInOut};
    opacity: 0;
    transform: translateY(-200%);
  `;
  const [exit, setExit] = React.useState(false);
  return (
    <>
      <div css={exit ? animatedItemExiting : animatedItem}>
        <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);

Emotion keyframes documentation: https://emotion.sh/docs/keyframes