About company
Funnily enough, browser support seems to be inconsistent for the last example. When border-image-slice is declared in advance and there’s no value for slice set in the border-image shorthand, as in the example above, Firefox 64 and Safari on iOS 12 uses the default slice value (which is 100%, resulting in border-image:
100%;) while Chrome 71 and Opera cascades the previously declared value into the shorthand (which gives border-image: 1;).
Mission
Shorthands do normally reset the longhands to their initial values when left out, so I don’t know why Chrome and Opera wouldn’t. The last example seems to be fixed in iOS12 by changing border-image to border-image-source in those two classes.
