Brian here from the Shopify support team :)
I can show you how to do so. Follow these steps and you will learn how:
- In your Admin, go to Online Store > Themes > Beside the blue Customize theme button, click the button with the three small dots and then choose this option "Edit HTML/CSS".
- In the Assets folder, choose the theme.scss.liquid file.
- Take a look at this screenshot for an example of what you then need to do - http://take.ms/jkv6M. When you are reducing the percentage, save the change, and refresh your website to view the change. If you want to adjust the percentage again, go back to the file and do so until you are happy with the play button's positioning.
This will help you out Matt, and if you have any more question do not hesitate to respond to this forum post or contact our live support :)