Wordpress - CSS not updating in browser when I change it

Add a random version number at the end of the css file you are attaching. If you are using 'wp_enqueue_style' or wp_register_style functions, pass a random (version) number rand(111,9999) to 4th parameter. If you are attaching css as an html tag, you should add "?ver=<?php echo rand(111,999)?>" at the end of the file name. Examples are here

wp_register_style( 'custom-style', get_template_directory_uri() . '/css/custom-style.css', array(), rand(111,9999), 'all' );

or

<link rel="stylesheet" type="text/css" href="http://website.com/css/custom-style.css?ver=<?php echo rand(111,999)?>">

It will avoid caching on client end caching and possibly server caching too.

I know this post is over a year old but I thought I would mention that CloudFlare caches static files such as css, js and images to aid in faster loading times. Something I just took hours to figure out, since I was having issues with my css changes not reflecting on reloading. CloudFlare has Development mode that you can enable for 3hrs. If you forget to enable it before you start making modifications then you can purge cache from cloudflare management.