center - to left margin - to center for submit button form

[schuyler1d]

With one question here: https://act.moveon.org/survey/readytoresist6/?template_set=main-giraffe

Not the biggest deal, but seems a little awkward especially when there's a single question

cc: @mstephani

[mstephani]

Now that all questions take 100% of the content width this should look better, if the question text is a checkbox or a radio the text should be long to look as intended on the comp