Inside the CSS code they add a CSS variable which stores the URL location of the web skimmer code they want to load inside a hacked store.

A CSS framework is a prewritten collection of CSS code designed to simplify and standardize web design. It typically includes styles for common elements such as buttons, forms, grids, and typography.

The CSS code isn't very complex and tries to apply a CSS effect known as backdrop-filter to a series of nested page segments (DIVs). Also: Best Home Security Devices for 2018 CNET ...