To me, the semi-transparent header and border are absolutely unacceptable. Imagine opening a book and 20% of the page are decor, decor with text no less. In clear words: this fucks with my attention, and the reason is that this is design that serves no actual purpose. If you're building a house or a product, anything that's not necessary is detrimental to the users experience, I don't even understand what can be argued about this
> Imagine opening a book and 20% of the page are decor, decor with text no less.
Regularly happens in "book world". Chapter headings are often an entire page, and sometimes even a double spread. The average whitespace around headings on the three closest books at hand were all 1/3rd of the page, making that decor even greater than the 20% you're describing.
House of Leaves is a book like this and the story is not the same without it. The words move down the page in a staircase fashion as Will Navidson is walking down the stairs to his untimely demise, in one example.
