3-theme-calculator-app using flex and grid structure

By default the font size is 16px, so 1rem is 16px, but it makes calculations difficult, like for 20px it's 1.25rem, 25px = 1.5625rem html { font-size: 62.5% } This 62.5% changes default font size to 10px, so 1rem becomes 10px and it's easy for calculations like 20px = 2rem, 16px = 1.6rem, 25px = 2.5rem.

Any suggestions appreciated...