content - CSS: Cascading Style Sheets
rete formal syntax normal | none | [ <content-replacement> | <content-list> ] [/ <string> ]?where <content-replacement> = <image><content-list> = [ <string> | contents | <image> | <quote> | <target> | <leader()> ]+where <image> = <url> | <image()> | <image-set()> | <element()> | <paint()> | <cross-fade()> | <gradient><quote> = open-quote | close-quote | no-open-quote | no-close-quote<target> = <target-counter()> | <target-counters()> | <target-text()><leader()> = leader( <leader-type> )where <image()> = image( <image-tags>?
...)<gradient> = <linear-gradient()> | <repeating-linear-gradient()> | <radial-gradient()> | <repeating-radial-gradient()> | <conic-gradient()><target-counter()> = target-counter( [ <string> | <url> ] , <custom-ident> , <counter-style>?
... )<target-counters()> = target-counters( [ <string> | <url> ] , <custom-ident> , <string> , <counter-style>?

CSS reference - CSS: Cascading Style Sheets
ap-stopscroll-snap-typescrollbar-colorscrollbar-width::selectionselector()sepia()<shape>shape-image-thresholdshape-marginshape-outsidesize (@page)skew()skewx()skewy()::slottedspeak-as (@counter-style)src (@font-face)steps()<string>@stylesetstyleset()@stylisticstylistic()suffix (@counter-style)@supports@swashswash()symbols (@counter-style)symbols()system (@counter-style)ttab-sizetable-layout:targettarget-counter()target-counters()target-text()text-aligntext-align-lasttext-combine-uprighttext-decorationtext-decoration-colortext-decoration-linetext-decoration-skip-inktext-decoration-styletext-decoration-thicknesstext-emphasistext-emphasis-colortext-emphasis-positiontext-emphasis-styletext-indenttext-justifytext-orientationtext-overflowtext-renderingtext-shadowtext-transformtext-underline-offsettext-underli...