Css styles for WordPress admin in functions.php

If you need to add individual styles, and they are only a couple of lines, you can add them directly to functions.php:

add_action('admin_head', 'webinp_style');
function webinp_style() {
print '<style>
tr[data-slug="to-top"] {display: none !important;}
</style>';
}

Between <style> and <style> you need to write your own CSS styles.