When i was a little kid, I was really scared of the dark. But then I came to understand, dark just means the absence of photons in the visible wavelength -- 400 to 700 nanometers. Then i thought, well, its really silly to be afraid of a lack of photons. Then i wasn't afraid of the dark anymore after that.
Elon Musk

block-size

The block-size CSS property defines the horizontal or vertical size of an element's block, depending on its writing mode. It corresponds to either the width or the height property, depending on the value of writing-mode.
block-size css reference