Is your WordPress style.css style sheet not updating in WordPress, even after clearing your cache? You may just need to update the version number.
Change your enqueued style sheet's version number
In your WordPress theme’s function.php file, if you have a line that looks similar to the one below; referring to the CSS style sheet you’ve recently edited. Try to increase the version number by 0.0.1.
wp_register_style( 'stylesheet', get_template_directory_uri().'/style.css', array(), '1.0.0', 'all' );
For example, 1.0.0 becomes 1.0.1.
Clear cache or use another browser
Manually clearing local cache
You could try to clear your cache by pressing Ctrl, Shift and R on your keyboard (Cmd, Shift and R if on a Mac).
Clearing plugin based cache
You could try to clear any plugin-generated cache or disable these cache plugins altogether.
Try to use another browser
You could try to use another browser (Chrome, Firefox, Safari, etc.).