How Best to Customize Your Site with CSS

As a developer, and trainer, my course of action when building a site for a client has been to use the current default WP core theme. Create a Child Theme and build out from there. To really accomplish this task requires the need of custom CSS page.
This is a very easy task to accomplish simply by adding a line of code in the header.php page. However, I have come to accept that the use of plugins is important when we look at updates. By employing a Plugin we lessen the chance that an update to the core theme will have any effect. And that if down the line the End-User moves to new them, that the plugins move with it.
In this case, way back when I found a Plugin called MyCSS that did the job. WordPress was at Version 2.5.
This plugin worked great until a later release and the developer did not update the plugin. So, I modified the plugin to work and have been using it since. It simply provides access to a custom.css page that I can access via the Dashboard or via ftp.
The issues that I have with the plugin are that when I click Save, the page relocates to the top of the, not maintaining my current position. And secondly, it would be very helpful to have line-numbers as most developer tools (Firebug) show line numbers.
So, I had some free time and did another search, albeit seven years later, for a custom CSS plugin.
And to my surprise, one exists that does exactly what I need. A custom CSS page, line numbers and keeps me positioned where I am when saving.
It is called Simple Custom CSS by John Regan and Danny Van Kooten. Overall it is seems to work great and is as simple at it gets.
Of the drawbacks, if there is to be one, is that I can no longer edit the custom.css page in a ftp editor. Which makes updating and viewing easy with two windows. However, I can accomplish the same with two windows and instead of the editor, the WP app page. An advantage of this method is that the css is all backed-up as part of the WP and does not require backing up an external file.
So, if you need to do custom CSS, then this is the plugin. And again, don’t forget to Donate.