How to reference an existing css content-based icon, within my admin menu hook

WordPress uses Dashicons. Basically you would replace your code with this:

add_menu_page('Cool Plugin Page', 'Cool Plugin', 'manage_options', 'my_main_menu','my_main_plugin_page', 'dashicons-admin-post', '');

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)