I’d like to reduce the space between the two lines of text but cant figure out what CSS selector and attribute I should modify. (apparently I don’t even know how to phrase the question to get the answer from google. 
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@kinozoom - can you please share your website link?
@kinozoom - please add this css to the very end of your base.css file and check,
Shopify Admin → Online Store ->Theme → Edit code → base.css
.rich-text__caption{margin-top: 5px;}
can I only change it in the base.css ? What if I want the change only to that one collection template?
@kinozoom – then use section id, so it changes this section only, like below
#shopify-section-template--18636506497249__f940af6a-8a70-4763-8ece-99e5405275ce .rich-text__caption{margin-top: 5px;}