That’s cool if true but until you try it you could be fooling yourself. The other thing is that it’s not really a skill that’s valuable in such a connected age, except in contrived scenarios like closed book coding interviews, maybe.
However my confidence that I could do this slowly and of poor quality is that - I started making websites 20 years ago so making and index.html file and linking to each file by hand and I still do this every now and then when making little static sites (like if a site is 4-8 pages I might just do it by hand). And the stuff I look up for sites like that are generally - how do I do this cool thing in CSS.
Admittedly if I did it this way the site I am envisioning doesn't look much better than Berkshire Hathaway's https://www.berkshirehathaway.com/
on edit: also there is some question if one is just allowed to do what one can remember in one's head or if, without using an internet search engine, one can use the stuff one has on local computers and devices? In which case I have some complicated stuff here to reference going back a lot of years, a lot of ebooks, local hardcopy books. So in that case I think I can do just about anything that can be done with search (except for using newest CSS, es2019 features), but still significantly slower.
If I was allowed to look at what I already have on my machine I could even set up a build process for my site. If not allowed then no build process.
But it would probably be pretty slow to write this, depending on how basic the site was, and it would not be as good as if I could look things up when I needed to.
But I wouldn't be able to deploy without searching.