Power BI offers a system that you can use to easily share and apply a theme to multiple reports. This feature is fully documented here: Use report themes in Power BI Desktop
In a few words, a theme consists of a series of appearance settings, such as a global font family or text color, along with specific visual properties, such as the axis color of a line chart. You can define these properties in a JSON file that represents the theme.
Unfortunately, custom visuals properties cannot be included in report theme files, as no official APIs are yet available to support them.
The only custom visuals properties that can be controlled through a theme are colors.
The following OKVIZ visuals support report theme colors - click the links below for information on how to configure them on a case-by-case basis: