This is the answer for this lesson. I was confused where to put the value at whether it was in div or div:hover.
<!DOCTYPE html>
<html>
<head>
<title>CSS transition-duration</title>
<style>
div {
width: 100px;
height: 100px;
background: #4535aa;
transition-property: width, height;
transition-duration: 2s, 4s;
transition-timing-function: ease-in, ease-out;
}
div:hover {
width: 300px;
height: 300px;
}
</style>
</head>
<body>
<div></div>
</body>
</html>
