What you're building
Use the :hover pseudo-class to change something — a button, a link, a card — when the cursor lands on it. This is where "static web page" becomes "interactive web page."
How the editor knows you're done
The code contains :hover somewhere in the CSS.
A starting point
Add this to the CSS panel (assuming you have a <button> from Challenge 2 — if not, drop one in first):
button:hover {
background: #1d4ed8;
transform: scale(1.05);
transition: all 0.15s ease;
}Move your cursor over the button in the preview. The transition line is the secret sauce — without it the change snaps; with it, it glides.