CSS page breaks in epub are a mess. I've tried to make them them work across ADE, Thorium, Calibre and Apple Books.
"break-after:column" is the modern property that is most widely supported (this requires column-fill: auto !important to be set for html and/or body). There is also "break-after: page" (sounds like it was intended for books) but they are not compatible with each other. When using both variants, the second one will override the first, no matter if it does anything or not. Kinda obvious, because it's the same property.
"break-after: always" and "break-after: all" are supposed to break after pages and colums. They didn't work in any reading software I tried.
There's also the legacy "page-break-after". It generally considered good practice include it for backwards compatibility. But apparently it can also override the page-break property.
Here is a little compatibility chart:
Code:
ADE Thorium Calibre Books
break-after: always - - - -
break-after: all - - - -
break-after: page - - - x
break-after: column x x x -
page-break-after: - - x x
and here is what happens if you combine them:
Code:
PBA/BAC: x x x -
PBA/BAP: - - - x
BAC/PBA: - - x x
BAC/BAP: - - - x
BAP/BAC: x x x -
PBA/BAP/BAC: x x x -
PBA/BAC/BAP: - - - x
BAP/BAC/PBA: - - x x
BAC/BAP/PBA: - - x x
BAC/PBA/BAP: - - - x
BAP/PBA/BAC: x x x -
"break-after: left;", "break-after: right;", "break-after: recto;" and
"break-after: verso;" would be useful for books, but I haven't found any reading software that supports them, either.