Looking to access your theme's code or language options with Shopify's new theme editor layout?
In your Shopify admin click on Online store > Themes
Next to the theme that you want to edit click on the Menu button which is a small square with 3 blue dots
This will open a submenu of options which includes: Edit HTMl / CSS and Edit Language
This is a safeguard to keep anything bad from happening to your site in the event of a mistake.
If you are attempting major changes then you will need to enter the Edit HTML / CSS section of the admin to gain access to all of the theme templates and assets.