There are several ways to find out what Shopify theme a website is using. Here are some methods:

1. Shopify Theme Detector: This is a web application that allows you to quickly find out which Shopify theme is being used on any given Shopify store. You can enter the stores URL and get instant results about which theme is being used.

2. View Page Source: When youre visiting a Shopify store using Chrome, you can right-click anywhere on the page and choose "View Page Source". Youll see the sites code. Use the search box and find the "Shopify.theme" string that includes the name and ID of the Shopify theme in question.

3. Shopify Theme Detectors Chrome Extension: There are several Shopify theme detectors among Chrome extensions. The most informative one is Koala Inspector. After you install it, you can click on the extension icon and it will show you the Shopify theme being used on the current website.

4. Contact the Store Owner: If none of the above methods work, you can try contacting the store owner and asking them which theme they are using.

In summary, there are several ways to find out what Shopify theme a website is using, including using a Shopify theme detector, viewing the page source, using a Shopify theme detectors Chrome extension, or contacting the store owner.