Styles can promote consistency or standardization across multiple maps and scenes within a project. ArcGIS Pro includes installed system styles that you can connect to from a project. These are read-only; you cannot modify their contents. You can also create and add your own styles to projects to organize style items to suit your work. Items from system styles can be copied to custom styles and modified as desired, or you can create new style items.
A project can include any number of styles. Styles that are added to a project are called project styles. When searching for symbols and other style items, you can choose to limit the search results to project styles only, or search from within all available styles included with ArcGIS Pro. You can remove any of these styles from the project (or connect to others) at any time. Removing a style does not have any impact on symbols or other assets you have accessed from that style and placed in a map, scene, or layout.
Styles are not dependent on the current map document; items you save into them will still be accessible when you open a different map document. Also, there is no reference maintained back to the style once a style item is applied. When you select and apply a symbol, a copy of the symbol is embedded within the layer or map document. Subsequent changes you make to that symbol in your map are not reflected in the copy stored in the style. Similarly, if you later modify the symbol in the style, the change will not propagate to the symbol embedded in your map. This means you don't need access to the original styles to open and draw a map again.
Default project styles
When a new project is created, connections to four system styles are made to provide a gallery of versatile symbols: ArcGIS 2D, ArcGIS 3D, ArcGIS Colors, and ColorBrewer Schemes RGB. As with any other project style, they can be removed at any time if their contents are distracting or otherwise unwanted in the galleries.
Your Favorites style is always available in a project; it can't be removed. It is linked to your user account, not the project. Items you store in it will be available across projects. You can use it to store style items you use frequently or as a testing area for working with styles. The Favorites style is not included as a project style when you package or share a project.