CSS styling for post pagination

I have pasted this code to my function.php file. But i want to make links circular and increase size of the links.
The code is:-
function custom_pagination( $content ) {
if( is_singular() ) {
$content .= wp_link_pages(‘echo=0’);
}
return $content;
}
add_filter( ‘the_content’,’custom_pagination’, 1 );

Please help.