border 0.5px with rounded corners not show on mobile display

Question

I tried:

border: 0.5px solid #efefef;
border-radius: 5px;

Result: only rounded corners line can not see

So I wonder 0.5px line works on mobile display.

I already have a UI with 0.5px lines and rounded corners and this works fine: it's looks ok

Why do some things work well and others not?

I don't want a CSS Tricks, So I modify border line to 1px. but I wonder why this happens

I would really appreciate it if you could help me