How to specify custom format

[brichards64]

Hi trying to figure out how to specify a custom style file

iv tried every combination of:

style: file <local_path_to_file>
style: <local_path_to_file>
style: file '<local_path_to_file>'
style: 'file <local_path_to_file>'
style: '<local_path_to_file>'

nothing seems to have worked, so any advice on this would be great