Welcome to the Shopify Community! Great idea having a unique, large call to action (CTA) on your page. Call to actions are extremely important, and having a well designed CTA can make a noticeable difference in your conversions. While coding something like this is out of my scope of support, I thought I'd comment on a couple alternate options for you, in case another Community user doesn't reply and assist you.
First of all, you could always post a (paid) job request in our Jobs & Careers board in the Community. Lots of users comment on these posts looking for paid work. Secondly, you can always hire a Shopify Expert to assist you. Shopify Experts are hand-selected partners that are proven to have an in-depth knowledge of Shopify. You can hire an expert for projects big or small; they have expertise in setup, development, marketing, design, photography and more.
Hopefully another Community user will reply and share some instructions on how you could code this yourself onto your store, but if not, I wanted to offer a couple other options to help find a solution. All the best!