CSS Code Desktop version to not affect Mobile version

Site URL: https://www.fadedbycs.com

Is there a CSS code that allows me to alter the Desktop version without the Mobile version getting affected size wise?
I want to change some positioning on the Desktop version but when the mobile one updates, it doesn't look as I expected!

Thanks!

Wrap your CSS code in media query

@media screen and (min-width:768px) {
paste your CSS code here.
}