Why is there an empty space after the footor?

Question

HTML

train.prospekt.pro/portfolio.html
Why in firefox when reducing the size of the site after the footor there is an empty space?

Answer 1

.section_2 {
/* сумма высоты футора и ходора */ 
min-height: calc(100vh - 274px);
}

Answer 2

Because the site is over, if there were more blocks in the content, it would be fine

Answer 3

That is why you need to make sure that the sum of the header footer and 1 line of text must be greater than the minimum vertical screen size, in which case there is no such problem in principle