Inheritance

• When you assign the master page and CSS file to the root site, you may choose to have all subsites inherit the same master page and/ or CSS.
• If you do not want a subsite to inherit the root settings, navigate to the Master Page settings for that subsite and choose a different master page or CSS file. This is useful if you need to apply a different color scheme or other visual changes to a subsite.

CSS File Positioning

How it looks. But, this page is not Home page. Click "Home" page.

Select Webpart page