Recurring contributions frequency label ("every month") is unstyleable - looks bad
You can add some css for the label tag that copies the style of the other text. Some margin or padding css on the link tag will take care of the spacing issue. As to the div.content, just be more specific on your selection so it only styles the labels you want to style. You should be able to select deeper than the div.content for those labels Or you might have to start your selection all the way up at the specific page to keep it from impacting the rest of the site. 

There is no way around it, you might have to make adjustments in the future if your theme changes (just like you said).