There is a simple CSS media query with which we can specify styles only for dark mode or light mode.

For specifying CSS when dark mode preference is selected.

@media (prefers-color-scheme: dark) {
    body {
        background: black;
        color: white;
    }
}

For specifying CSS when light mode preference is selected or no active preference has been expressed.

@media (prefers-color-scheme: light) {
    body {
        background: white;
        color: black;
    }
}

Original posting: https://twitter.com/varun_barad/status/1190613832575725571