How to update total stock across multiple designs on Shopify?

I am currently setting up my Shopify website for my clothing brand, and I want to update my stock differently. I am selling a total of 100 shirts that can have five different designs depending on the design that the customer orders. I was just wondering how I can depict this on Shopify, as the inventory section on Shopify only allows me to update stock for individual products. So instead of showing that there is a total of 100 shirts, it shows that there are 500 shirts in total, with 100 shirts for each design. Ideally, the stock is 100 in total, and when a shirt is bought, it deducts 1 and updates this on every page.