Best tool to validate UI mockups by overlaying them

I'm looking for a solution/tool that will allow me to validate that my frontend project is pixel-perfectly aligned with the Photoshop mockups.

Best would be to make the browser window transparent - that way I could lay it over the mockups and see if they align as they should. Unfortunately, I cannot find such a tool for MacOS. Safari used to have "Use transparent window" debug feature, however it's missing in Catalina. There used to be tools like afloat and afloax however they don't work with Catalina - and even if they did, they need to disable SIP, which is impossible in corporate environment for security reasons.

Any ideas?