What is underscroll?

How do you under scroll?

To "underscroll," which typically refers to scrolling down a webpage or document to view content that is not immediately visible, you can use a mouse scroll wheel, trackpad gestures, or keyboard shortcuts like the down arrow key or the spacebar. On mobile devices, you can swipe up with your finger on the screen. If you're referring to a specific programming or design context, please provide more details for a tailored response.