In brief
border-right sets the right border's width, style and colour. In a multi-panel interface, it can act as a one-sided separator.
Useful to know
border-right sets the right border's width, style and colour. In a multi-panel interface, it can act as a one-sided separator. [1]
This physical side does not automatically switch with text direction. If the design should follow inline start or end across languages, compare logical properties and check the complete component.
Sources
For further detail and to check the information: