Add detection of preferred color schemes

[wcoder]

New standard is registered on W3C in Media Queries Level 5.

Example:

/* Light mode */
@media (prefers-color-scheme: light) {
    body {
        background-color: #000;
        color: white;
    }
}

/* Dark mode */
@media (prefers-color-scheme: dark) {
    body {
        background-color: #000;
        color: white;
    }
}