Mobile Header Menu Not Collapsing Properly

Store Design

Topic summary

A user reports that their header menu fails to collapse into a hamburger icon on mobile devices while using a customized Debut theme.

Potential causes identified:

  • CSS breakpoints may have been altered or removed during customization, preventing media queries from triggering mobile layouts
  • JavaScript functionality could be broken or missing, particularly in theme.js or theme.js.liquid files that control menu toggling
  • Header structure modifications in header.liquid may have removed critical classes or data attributes

Recommended troubleshooting steps:

  • Inspect media queries in theme.scss.liquid for proper mobile breakpoints
  • Verify hamburger button markup exists in header.liquid with correct classes like js-drawer-open-left
  • Confirm drawer logic JavaScript is present and functional
  • Test by temporarily reverting header.liquid and theme.js.liquid to default versions

Important clarification: If the issue occurs only on checkout pages, this is expected behavior for standard Shopify plans, as checkout customization requires Shopify Plus. The discussion remains open with offers to help debug specific code files.

Summarized with AI on October 29. AI used: claude-sonnet-4-5-20250929.
1

Hi, I’m having an issue where my header menu doesn’t collapse into a hamburger menu on mobile devices (Checkout). I’m using a slightly customized version of the Debut theme. Any ideas on what could be causing this?

2

It sounds like there may be a conflict or missing element preventing the mobile hamburger menu from functioning correctly on your site

The issue could also be related to CSS. Check if there are styles overriding the default mobile menu behavior.

3

Hi there! Great question.

If your header menu isn’t collapsing into a hamburger menu on mobile, and you’re using a slightly customized version of the Debut theme, it’s possible that the customizations may have impacted the responsive behavior.

Also, it’s worth noting that the checkout page uses a separate layout controlled by Shopify, and custom theme styles or scripts typically won’t apply there so that could also be affecting what you’re seeing.

If you’re comfortable sharing a bit more detail—like whether this happens only during checkout or across your site—it might help others in the community provide more targeted suggestions!

4

Hello James, permit me by first commending you on the store design, that’s a nice design right there.

For the Header Menu issue, here’s What Might Be Going On:

When the header menu doesn’t collapse into a hamburger menu on mobile, it’s often caused by one of the following:

1. CSS Breakpoints Might Be Altered

If you’ve made style changes, it’s possible that the media queries (the rules that trigger mobile layouts) were changed or accidentally removed. That could stop the hamburger menu from appearing when the screen gets smaller.

2. JavaScript Not Running Properly

The Debut theme uses JavaScript to toggle the menu open and closed on mobile. If you’ve customized your theme, it’s possible that some required JavaScript has been broken or removed — especially in theme.js or theme.js.liquid.

3. Header Structure Was Modified

Even small edits to header.liquid can throw off the layout. If certain classes or data attributes were removed or renamed, Shopify’s built-in mobile menu logic won’t know what to do.

What You Can Try:#### Inspect Your Media Queries

In your CSS (usually theme.scss.liquid), search for media queries like:

css

CopyEdit

@media screen and (max-width: 749px)

 

Make sure the styles for .site-header and .site-nav still contain logic to hide the full menu and show the hamburger icon.

Check for the Hamburger Button Markup

In header.liquid, look for something like:

html

CopyEdit

… 

 

If it’s missing or edited, the menu toggle won’t appear or work. Even changing a class name can break it.

Make Sure JavaScript Is Loaded

In your theme.js.liquid, check that the drawer logic still exists and hasn’t been removed:

js

CopyEdit

$(‘.js-drawer-open-left’).on(‘click’, function () { Shopify.Drawers.open(‘nav’, ‘left’); });

 

If you don’t see this, or it’s commented out/broken, the mobile menu won’t function.

Final Option: Revert Partially to Default

If things still seem off, you might want to temporarily restore a clean copy of header.liquid and theme.js.liquid from the original Debut theme to test — just to see if the issue disappears. That can narrow down what customization caused the issue.

5

Shopify’s checkout pages are locked down — you cannot fully customize them unless you’re on Shopify Plus. So if your mobile menu works on the rest of your site but not during checkout, that’s expected behavior for non-Plus plans.

However, if you see issues outside the checkout page too (like on your homepage or product pages), that’s likely related to theme customizations or JavaScript issues.

Let me know if you want help checking specific code files or if you’d like to FIX your header. liquid or theme.js code — I can debug it with you.