Creating a style can be time-consuming, and all that work can be lost (e.g. if you accidentally delete a style). Fortunately, it is possible to save the style to a file and use it in another layer.
To save the style, select the three dots and the Export Style option. The file with the extension .aq3 will be saved to disk.
It is System-specific and cannot be used in other GIS software. A saved style can be imported (read: Style Import).