How to display a line on fixed length mobile screens?

Question

css

Now there are many new different devices. The question is quite simple.
How to display a vertical line with a length of, for example, 10 centimeters? To have 10 cm on all mobile devices? width: 10cm
How can this be tested if there are no real devices?

Answer 1

Understood, I not absolutely correctly asked a question.
It is better to do everything through media to adapt to different screens.

// Extra small devices (portrait phones, less than 576px)
@media (max-width: 575.98px) { ... }

// Small devices (landscape phones, 576px and up)
@media (min-width: 576px) and (max-width: 767.98px) { ... }

// Medium devices (tablets, 768px and up)
@media (min-width: 768px) and (max-width: 991.98px) { ... }

// Large devices (desktops, 992px and up)
@media (min-width: 992px) and (max-width: 1199.98px) { ... }

// Extra large devices (large desktops, 1200px and up)
@media (min-width: 1200px) { ... }