You can use wp_add_inline_style()
.
Let's assume you enqueue your css like so
add_action( 'wp_enqueue_scripts', 'add_my_style' );
function add_my_style() {
wp_enqueue_script( 'my_style', get_template_directory_uri() . '/mystyle.css' );
}
Then you can change the function like so:
function add_my_style() {
wp_enqueue_script( 'my_style', get_template_directory_uri() . '/mystyle.css' );
$style = "#mainnav li:after { content: url('{theme_url}/images/nav-divider.png'); }";
$style .= "#another-example { content: url('{theme_url}/images/example.png'); }";
$data = str_replace( '{theme_url}', get_template_directory_uri(), $style );
wp_add_inline_style( 'my_style', $data )
}
wp_add_inline_style()
to alter the#mainnav li:after
style once your stylesheets have loaded.