Have you ever visited a WordPress website and found that articles in different categories had different styles and designs like different backgrounds, fonts, text colors, …? For example, in a music blog, the articles in the “Blue” category have a dreamy purple background, and the articles in the “Rock” category have a dark color. This is an interesting highlight in the design, making your website more impressive in the eyes of viewers.
Meta Box's custom fields have a default padding, color, border, font, etc. which may not fit your design in either back end or front end. So you may want to change how they display, making them more eye-catching. That's the moment you want to style them.
So do the custom fields created by Meta Box. You definitely can style every custom field created by Meta Box as you want. In this post, I will give you some way to use CSS to style the fields.