Custom Macro Buttons in Excel 365

So - As a user of Excel 2003 (Yes - 2003) I have created quite a few macros and attached these macros to buttons that I have modified. Nothing fancy, as you can see by the attachment, just images that work for my team and I.

I am starting to use Excel 365 and I find that I can still use these macros but if I want to attach them to button images, I have to choose one from a list rather than creating the button image that we are used to.

Do I have any options? Can I add modified images to where ever excel 365 stores the pre made buttons?

Any help would be appreciated.

Jim