Assuming there is a Parent Table,
Create a summary from the parent table called something like [# of Styles] then pull that summary field back down to the catalog/styles table.
Then create a numeric formula field with [# of Styles] + 1 and call it [Next Style #]
Make sure you have a text field on the form for "Style #"
Then just create a dynamic form rule that says, "If [Style #] is blank, change [Style #] to the value in the field [Next Style #].
Make sure you uncheck the box that says "Fire on change"
Now you should be able to change the style number manually if need be, while also having it auto-increment to the next number if you don't need to ever set it manually.
Alternatively, you can just use the record ID# as it auto-increments natively.