Dressing up a screenshot with padding and a shadow
A raw screenshot reads as a raw screenshot. The browser chrome is still sitting in the corners, there's no background behind it, and it fills the frame edge to edge in a way that catches the eye for the wrong reason.
Padding, a background, a shadow, and rounded corners fix most of that on their own. This is the whole feature that tools like Xnapper and CleanShot charge for, and the line that shows up over and over in reviews of both is that it makes the person's work look like it came from a professional.
Padding is a ratio, not a pixel count
Padding here is set as a share of the shorter side, not a fixed number of pixels. Wrap 48px around a 1920px screenshot and it barely registers — a tiny fraction of the frame. Wrap that same 48px around an 800px screenshot and the padding eats 6% of the image, which reads as obviously too much. Scaling by the shorter side keeps the padding looking consistent no matter what size screenshot comes in.
JPG can't hold transparency
JPG has no concept of transparency at all. Set the background to "none," turn on rounded corners, and export as JPG, and the spot outside the corners should be empty — so this tool fills it with white automatically instead. You don't need to pick a background color yourself just to avoid black corners; PNG or WebP keep the transparency instead, if that's what you want there.
The shadow falls one direction
The shadow here drops downward, the way a card looks like it's lifted slightly off the surface behind it — useful when you want the screenshot to read as visually separate from its background rather than flush against it. A heavier shadow reads as more lifted; a lighter one reads as closer to the background.
The original never changes
Toggling padding and shadow on and off while you preview doesn't touch the image file. What you're seeing is a preview laid on top of it; the actual pixels only get redrawn in that shape once, at the moment you export. Turn the styling on and off as many times as you want — the photo underneath never degrades, and you can always get back to the plain original.