Keeping your sub-sites congruent to the prescribed theme is an important way for your end users to keep track of where they at. Aesthetically, end users will begin to associate certain colors and themes with the work area they are visiting.
This change is easy to accomplish and can be done in a matter of a few clicks.
1. Browse to site your wishing to edit.
2. Copy and paste the following: “_layouts/15/ChangeSiteMasterPage.aspx” to the end of your SharePoint Page.
So your page should look something like this “https://yourcompany.sharepoint.com/testsite/_layouts/15/ChangeSiteMasterPage.aspx”
3. You’ll want to inherit from the parent page.
The following is an example of how you’ll inherit from the parent site page. It’s as easy as selecting the following three options.
Inheriting the theme is important to remember, otherwise your site will inherit the feature but will not have the same stylistic feel as the site your inheriting from.
4. Click “OK”
Your changes may take a few seconds to load. Your new page should have that same look and feel as your parent site.