Frontend & browser·Layout, CSS and the cascade
you put `box-sizing: border-box` in the reset and every width in the codebase started meaning what you expected.
box-sizing
Also calledborder-box, content-box
The property that chooses whether a declared width includes padding and border. `border-box` makes width mean the outer size, which is what almost everyone means almost every time, and it is why nearly every CSS reset sets it globally. The one place `content-box` still matters is when a component must size to its content exactly and the padding is meant to grow it.