css in functions.php

if my theme’s stylesheet template does not contain styles and the last comment says this:

All styles and js scripts are now loaded in wp_print_style() and wp_enqueue_scripts() in functions.php

Does this mean that I can’t just make modifications by adding to the end of the sytlesheet?

For example something like this:

a {
    color: red;
    text-decoration: none;
}

If not, how would I make this same modification in the functions.php template?

Thanks!