border-block-end-color: red; 
writing-mode: horizontal-tb;

border-block-end-color: #32a1ce; 
writing-mode: vertical-rl;

border-block-end-color: rgb(170, 50, 220, .6);
writing-mode: horizontal-tb;

border-block-end-color: hsl(60, 90%, 50%, .8);
writing-mode: vertical-lr;