Some comic pages are tall enough to require a scrollbar, some are not. This means that on some systems (in my case, Firefox on Windows 10) the scrollbar appears and disappears. As it makes the page narrower, the content shifts, which can be distracting when going between pages.

I think all that's needed is applied to the body, which would force the vertical scrollbar to appear even when there is no need to scroll, and is documented as "prevents scroll bars from appearing or disappearing when the content changes" https://developer.mozilla.org/en-US/docs/Web/CSS/overflow-y#scroll

I've attached screenshots of what it looks like on my computer, the first and second images are what it looks like normally, and the third is when I add that bit of CSS with the inspect element tool to show what I'd like it to look like.