Selective changes (only for "standard" browser)

I have made some changes to the theme using custom CSS, such as making the sidebar a little more narrow, making the header fixed, etc.

This is working fine and displays great on a standard computer browser.

When accessing on a mobile platform, the layout does not look so good.

Is there any way I can limit these changes only to screens with a specific resolution, for example?

Basically, all custom CSS changes I am making I would like to apply only to a computer browser (or large enough resolution) and leave the theme untouched for mobile devices with smaller screens, if possible.

The URL is https://perceptualview.com

Many thanks!