I’ve used the plugin Orbisius Child Theme creator to create a child theme for this site. Using Child Themes is highly recommended when your are basing your site on an existing theme and all you need to do is change some of the styling with CSS and perhaps a few other adjustments. Creating a Child Theme will be one of the first things you do just after you install WordPress.
If you want to create a site from scratch, they recommend using a framework and then base a Child Theme on the framework. Genesis Framework is one example, but there are others.
Naming your child theme
If you want to keep the theme you used difficult to discover by people browsing your site, name your child theme in such a way that it does not include the name of the parent theme. You could use your first initial and last name to name your theme. If a user of your site were to use Inspect Element in Firefox, they could look into the head section and look at the link to the css style sheet that points to the child theme’s style sheet. It shows the directory path. WordPress stores themes in a themes folder:
WordPress Multisite Network
In order to edit a theme in a multisite WordPress environment you must do it from Network Admin > Appearance.