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!