I know what you are talking about. Projects tend to slow down at the end of it. But responsiveness is not one of those things, at least on this project. My honest guess is 3%, the menu being the biggest piece. It can also be lazily loaded so that it doesn't increase the amount of primary CSS. Just like the dark mode was implemented.
Having said that, I promise 100% feature parity on my next article. Thanks for the heads up!
Features that look easy to implement and are not a big deal can turn out to be massive problems and require a large amount of code to actually pull of. I would, in some cases, count responsiveness to be one of those things. Stuff like that may seem like 5% of the
functionality but actually makes up a large chunk of the code. This is why you must always have feature parity if you really want to compare code size.
