set a fixed maximum width for the grid.
This setting applies either to the widget container or to the widget depending on the ‘fitwidth’ setting.
The widget sits inside of a container. grid items sit inside of the widget.
If fitwidth is set: this setting is applied to the maximum width of the container. It defaults to 100%. The actual container width will stretch depend based on the size of the browser window but will never exceed the maximum width. The widget width itself is set based on content. This is the default recommended setting.
if fitwidth is not set: this setting is applied to the widget instead of the container and defaults to 100%. The container is always 100% (although this can be edited in your custom css or stylesheet). This setting is not recommended. Experiment with this setting in the widget. You will see that it works a little bit differently.
Set the gridwidth to 50% with fitwidth enabled:
[featured_image_pro gridwidth='50%' posts_per_page='4' ]
Set the gridwidth to 50% with fitwidth disabled:
[featured_image_pro gridwidth='50%' fitwidth=false posts_per_page='4' ]
Set the gridwidth to 400px
[featured_image_pro gridwidth='400px' posts_per_page='4' ]
Set the gridwidth to 400px with fitwidth disabled
[featured_image_pro gridwidth='400px' fitwidth=false posts_per_page='4' ]