Custom code is almost always the cause. A <style> block or a script in your header or footer runs on every page of your live store, so a small mistake is visible to every customer immediately.
Get the store back before you debug. The section toggle removes your code from the live store straight away, which buys you time to find the problem properly.
Step 1: Turn off the affected section
Open your custom code settings, disable the affected section using its toggle, whether that is Header or Footer, and save. Your code is removed from the live store immediately.
Do this first, before investigating. A broken store costs you orders while you read error messages.
Step 2: Fix the code in the test environment
Work on the code in your test environment rather than on the live store, then re-enable the section once it behaves.
Two things about the test environment catch people out. Its password is separate from your live Storefront and Reseller Control Panel credentials, and OpenSRS Support has to reset it for you if you have lost it. It also initialises from your live Storefront only at first login, so any change you have made to your live store since then has to be applied there by hand.
Step 3: Work out what the code is doing
Your browser's developer tools answer most of these questions faster than re-reading the code. Press F12 to open them.
CSS isn't taking effect
Confirm your <style> block is in the Header field rather than the footer, that the section toggle is enabled, and that you saved.
If it is all correct and the styling still does not apply, another rule is probably overriding yours. Open F12 → Inspector, select the element you are trying to style, and look at which rules are winning. Adding !important to your property resolves most of these.
Code is saved but does nothing
Check the toggle for that section reads Enabled and that you clicked Save, since an unsaved change looks identical to a broken one.
If it is enabled and saved, open F12 → Console and look for JavaScript errors. An error early in your script stops everything after it from running.
Analytics isn't recording
Open F12 → Network and reload a page to see whether the analytics request fires. If it does, the problem is at the analytics provider rather than in your store.
Most analytics tools also publish their own debugging extension, such as Google Tag Assistant for GA4, which is usually quicker than reading network requests.
When to contact OpenSRS Support
Contact OpenSRS Support when your store still renders incorrectly with every custom code section disabled and saved, since at that point your code is not what is wrong. Support also handles test environment password resets.
Related articles
Full Storefront documentation
These troubleshooting articles cover what to do when something breaks. Setup guides, feature documentation and the Storefront API reference all live on the Storefront documentation portal.