[Horizon] Auto-expand the current page's hierarchy and highlight the active item when opening the drawer menu

With the Horizon theme's drawer menu, when the navigation is deeply nested you have to trace back through the levels again to reach where you are. With this setup, the moment the drawer opens it automatically expands to the hierarchy of the page you're currently viewing, and the current page's menu item is highlighted with a gray background. The Dawn version is available here.

You don't edit any theme files (such as header-drawer.liquid) — just add a Custom Liquid section to the footer group and paste the code. It supports both the top-level slide panel and the in-panel accordion (the third level).

Result

Setup

◆Add a Custom Liquid section
・Open the theme editor and add a "Custom Liquid" section to the footer group.
・Paste this TIPS's code into the Liquid code field of the added section and save.

◆Notes
・The current page is detected using markers Shopify adds automatically (current page / active parent), so it keeps working even if you change the menu structure.
・The current-page highlight is always active once the code is added, so you can tell where you are even when navigating the menu manually.