Help with iFrame padding

Hello - I recently implemented a booking widget code (iframe) for clients to book directly through my client software, but I'm having some trouble with the appearance.

I *think* what I want is for some extra padding on the left (see image), or whatever the fix is to give more white space between the left edge, and the text/calendar dates. 

I've fiddled around with a lot of CSS and iframe, based on articles and forum information, but anything that adds padding to the left, pushes the text to the left edge, still.  So maybe this means it does not need padding, but rather a different alignment?

Please help!

Website is public: http://hilarybeckwith.com/inside-out

My testing

1 hour ago, Beyondspace said:

You can try adding to Home > Design > Custom Css

#block-yui_3_17_2_1_1665094218540_4516 iframe {
  border: 20px solid #fff !important;
  box-sizing: border-box;
}

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That did the trick, thank you!