I swear by the end of this article I will understand how mobile ADAPTS to those transformations

First, REM adaptation

750px is the width of the design, and the conversion ratio is 100, that is, 100px of the design corresponds to 1REM of the CSS, so we divide the design into 100 pieces, so the width of the design is 750/100REM in terms of CSS pixels, and the width of the design corresponds to the width of the visual palpability, that is

750/100 rem is 100vw so 1rem is 100vw over 7.5

Therefore, we can set the HTML font size to calc(100vw/7.5), and then divide the value of the design text by 100, and use REM representation.