Why at very low resolution (320x240px) the site is displayed only on a part of the window?

Question

css

Hello. I decided to make the fifth version of the site for screens with a width of less than 320px. First of all, I noticed that the paralax block (plugin) does not take up the entire width, unlike screens with 500px+ width. Why can this be? Moreover, the lower the resolution, the greater the "former artifact"
PS Block width 100%

Answer 1

Obviously, something (a block with words) gets out and stretches the screen.