Styles are 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 managed as items in a project. You can add as many styles as you want to a project.
Structurally, styles are databases that are stored as individual files in your file system or in a portal. There are different types of styles, as outlined in the following table.
| Type of style | Description |
|---|---|
AllSource style | The generic term for any style used in AllSource. They are stored locally or in a portal as single files but can be added to a project. AllSource styles have a .stylx file extension. |
Desktop style | Styles that are created in and used in ArcMap, ArcScene and ArcGlobe. These style files have a .style file extension. You can import them into an AllSource project. Once imported, the AllSource version of the style is placed in the project home folder (for example, [install drive]:\\Users\MyUserName\Documents\ArcGIS\Projects\MyProjectName), and added to the project. You can reference it from this location (or copy it elsewhere) from other AllSource projects. There is no need to import a desktop style more than once. |
Project style | Any style connected to the current project. Symbols, other element galleries, and color pickers are populated by the contents of the style items. So you can control what you see in these galleries by choosing which styles to add to a project. Project styles include any combination of your Favorites style, system styles, custom styles, web styles, mobile styles, and dictionary styles. |
Favorites style | Your Favorites style is always available in a project as it is linked to your user account. All other styles are connected to a project. Items in your Favorites style always appear at the top of galleries. Your Favorites style is not included when you package a project. The Favorites style is not to be confused with adding project items to project favorites. |
System style | The styles that are authored by Esri and included in the AllSource installation. Only a subset of system styles are added to each new project by default. These default systems styles are listed below.
System styles are read-only, but you can copy items from them to other styles and modify as necessary. System styles are not packaged with projects. |
Custom style | Any style that is not a system style is a custom style. You can add custom styles to a project or you can create new styles. Custom styles are editable by default, but you can make them read-only to prevent inadvertent changes. |
Web style | Web styles are styles shared to a portal from AllSource to make them available for web applications and mobile applications on the ArcGIS platform. You can consume a web style back into AllSource by adding it to a project. In this case, the style is read only and cannot be shared to a portal. |
Mobile style | Mobile styles are intended for use in mobile apps. They support fewer style item properties than AllSource styles. |
Project styles
All the styles in a project are collectively referred to as project styles. What you see in the galleries as you author maps and layouts is the contents of the project styles. Add and remove styles in a project to customize what appears in these galleries.
When a symbol or other style item is used somewhere in a project, such as a map or a layout, there is no reference maintained to the style. Instead a copy of the symbol or style item is applied. Any changes made to that symbol (or style item) are not reflected back in the style, and changes to the style are not propagated to the symbol (or style item). This means that you don't need access to the original styles to open and draw a map again. You can add and remove styles from a project at any time. Removing a style does not delete the style from the file location.
Favorites style
Your Favorites style 
is always available in a project; it can't be removed. It's linked to your ArcGIS user account, and not the project itself, so items stored in your Favorites style are available across projects. You can use Favorites 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.
Legacy:
Your Favorites style is similar to your Personal style in ArcGIS Desktop applications such as ArcMap.
System styles
System styles are those styles installed with AllSource. They're authored by Esri and are read-only, but you can copy the items into custom styles or your Favorites style 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 if you want their contents to appear in your galleries. When searching for symbols and other style items in galleries, you can limit the search results to only project styles, or you can search from within the project styles and all system styles included with AllSource.
Reference the AllSource Symbols PDF document to see a thumbnail image of every symbol and style item included in the AllSource system styles. See the Esri Styles organization for additional PDF documents of individual styles.
Legacy:
ArcGIS 2D and ArcGIS 3D are styles authored specifically for AllSource. They can be considered replacements for the ESRI, ArcSceneBasic, and 3D Billboards styles that are referenced by default in ArcMap, ArcScene, and ArcGlobe, respectively. The colors contained in these styles have been removed and placed into a third default style called ArcGIS Colors.
Custom styles
Any style that's not a system style is a custom style. Custom styles are authored by anyone and are editable by default. 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 are packaged. The system styles and your Favorites style are not included.
Web styles
You can share any custom style in an AllSource project as a web style to ArcGIS Online or ArcGIS Enterprise. 3D web styles are used in web scenes in the Scene Viewer symbol gallery. You can also share a 2D style or a style with dictionary symbology to ArcGIS Online and ArcGIS Enterprise to use in the ArcGIS API for JavaScript.
When sharing a style to a web style, you choose whether to share a 2D or a 3D style. When sharing as a 3D style, only point symbols composed of one 3D model marker symbol layer are included in the web style. All other style items are dropped. To share a 2D style, no symbols in the style can contain 3D model marker symbol layers and dictionary styles must be version 3.0.0 or higher. (See the dictionary toolkit for more information on dictionary versions.) For specific requirements, see Share a web style.
You can add a web style from ArcGIS Online or ArcGIS Enterprise to AllSource and use the symbols in AllSource projects. Web styles in AllSource are always read-only.
Mobile styles
Mobile styles are intended for use in mobile apps but can also be used in AllSource. Use mobile styles when authoring maps and scenes that will be shared to a mobile app.
Mobile styles have some limitations that standard styles do not. When 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 are vectorized, and a reference to the font is dropped. Similarly, any true curves present in shape marker layers are densified to simple vertices and straight segments.
You can create a mobile style in a project and create symbols in it or copy symbols from other AllSource styles. Complex symbols copied into a mobile style are downgraded to meet the mobile style requirements.
Import styles
You cannot use desktop styles (those used in ArcMap, ArcGlobe, or ArcScene) directly in AllSource because of differences in the underlying database structure. However, you can import a style into an AllSource project.
When you import a desktop style, an AllSource version of it is created in the project home folder (for example, [install drive]:\\Users\MyUserName\Documents\ArcGIS\Projects\MyProjectName) and added to the project. You can reference it from this location (or copy it elsewhere) from other AllSource projects. There is no need to import a desktop style more than once.
Legacy:
Some desktop styles have been converted to AllSource format and included in the installations as system styles. Others have been retired, but you can access AllSource versions of them from ArcGIS Online in the Esri Styles organization. In the Catalog pane, under the Portal tab, click All Portal 
and search for stylx to find all available style files.
Alternatively, if you have ArcMap installed, you can import any of the styles included in that installation to the AllSource format. On the Insert tab, in the Styles group, click Import 
and browse to [install drive]:\Program Files (x86)\ArcGIS\Desktop<version#>\Styles. Choose a style 
and click OK. An AllSource *.stylx version of the style is created in the project home folder and added to your project.
Legacy:
AllSource styles (.stylx) are not backward compatible and cannot be imported into ArcMap.