Looks like you can’t set separate styles for light mode and dark mode. It gets replaced with your last selection.
Steps to reproduce:
Create a div, enable Tailwind mode, set border style to solid, set width to 2, and set a border colour
Switch the canvas to dark mode. Select a new border colour.
Instead of getting both border-slate-300 dark:border-slate-800 classes, it only gets the dark class.
Border width has the same issue.
Border style doesn’t have the same issue, but does something funky. Sometimes if you change it from solid to none (or vice versa), it will just stack the classes: