Overlay your mockup image above the Browser or Simulator and spot the differences like wrong paddings and fonts.

The easiest way is to take screenshot from Figma/Sketch/Photoshop/XD — Pixel Perfect Tool monitors Clipboard and instantly displays copied image!
Or drag and drop image into the app icon.

Keyboard shortcuts:
“Arrows” — Move by one pixel (hold Shift to move faster)
“+/-” — Zoom (hold Option to zoom slower)
“R” — Reset zoom
“Ctrl+Shift+Command+4” — macOS shortcut to take screenshot to Clipboard
“1-9” — Change opacity
“0” — Full opacity
“~” — Toggle Hide