Subscribe Module Button Too Long

Could you let me know how to reduce the size of the 'Subscribe' button in the subscribe module. When I use the 'Form on Page' module behavior, the size of the button is a reasonable size and isn't larger than the text within the button. However, when I use the 'Dialogue Form' behavior, the button extends the entire width of the module instead of adhering to the text width inside the button. See attached example of each and notice the size difference with each behavior.

I hope this makes sense and I appreciate your time looking into this for me.

Sam