Styles are project item containers that store symbols, colors, color schemes, label placements, and layout items. They promote consistency and standardization across maps, scenes, and layouts. The symbol galleries and color pickers you work with when you author maps, scenes, and layouts are populated by items stored in styles. Styles are stored as individual files in your file system. You can add as many styles as you like to a project.
Styles are databases stored as individual files in your file system and then referenced by a project. They have a .stylx file extension. All the styles in a project are collectively referred to as project styles. When searching for symbols and other style items in galleries, you can limit the search results to project styles only, or search from within the project styles and all system styles included with ArcGIS Pro.
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. There is no reference maintained to the style once a style item is applied. When you select and apply a symbol to a feature, for example, a copy of the symbol is embedded in the layer. Subsequent changes made to that symbol in the layer are not reflected back in the style. Similarly, changes to the symbol in the style are not propagated to the symbol in the layer.
This means you don't need access to the original styles to open and draw a map again. You can add and remove project styles at any time. Removing a style does not delete the style from the file location. The project styles only dictate what you see in the galleries.
A project can contain different types of styles.
System styles are those that are installed with ArcGIS Pro. They are authored by Esri and are read-only. You can't make changes to them, but you can copy items from them into your own styles to modify them. Some system styles are added to new projects by default: ArcGIS 2D, ArcGIS 3D, ArcGIS Colors, and ColorBrewer Schemes RGB. Others are available, but you need to explicitly add them to the project.
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 the Favorites style will be available across projects. You can use it to store style items you use frequently or as a testing area for building new style items. The Favorites style is not included as a project style when you package or share a project.
Mobile styles are intended for use in mobile apps but can also be used in ArcGIS Pro. They have some limitations that standard styles do not. They are ideal when authoring maps and scenes that will be shared to a mobile app.
When mobile styles are used in mobile apps, all style items other than point, line, polygon, and text symbols are ignored. The symbols reference RGB colors only. Any shape marker symbol layers built from font glyphs will be vectorized, and a reference to the font will be dropped. Similarly, any true curves present in shape marker layers will be densified to simple vertices and straight segments.
Custom styles are authored by anyone and do not have the limitations specific to mobile styles. You can add custom styles to your project from your file system or from a portal. You can also author new custom styles. When you package or share a project, only custom project styles (including mobile styles) are packaged. System styles and your Favorites style are not included.
Styles used in ArcMap, ArcGlobe, and ArcScene cannot be used directly in ArcGIS Pro because of differences in the underlying database structure. However, you can import a style into ArcGIS Pro, which makes an ArcGIS Pro version of it and automatically adds it to your project.
Styles in ArcGIS Pro have a .stylx file extension and are shown with a icon. Styles in ArcMap, ArcGlobe, and ArcScene have a .style extension and are shown with a icon.