The layout broke after an edit
A page whose blocks have all stacked vertically, with no colours or spacing, has not lost its content: it has lost its stylesheet. That specific symptom has few possible causes, and the browser names them itself in a tab few people open.
The browser tells you what is missing
The developer tools built into every browser include a network tab listing each requested file and the response code received. A failing stylesheet shows there in red, with its full address. That is the decisive information: it says whether the file is absent, refused, or served empty.
A second tab, the console, shows script errors. A single error stops execution of everything that follows in the same file — which is why a menu, a carousel and a button can all stop working together because of one faulty line. Those two tabs usually answer "where did this break" in under a minute.
What I find behind this symptom
- The assembled stylesheet was not regenerated after the edit: it still refers to the old structure.
- Automatic file compression failed on a syntax error, producing a file truncated from that line onwards.
- An edit made in the parent theme while the child theme is active: the edited file is never loaded.
- A theme update overwrote customised files, because the changes had been made directly inside them.
- A module added its own stylesheet after the theme’s, and its rules override the intended ones.
Getting back to a healthy state
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Identify the scope
One page, one page type, or the whole site? A fault on every page points to a global file; a fault on one page points to content or a module specific to it.
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Look at the network tab
Spot the failing files. A failing address means a path that has become wrong, often after a site move or an address change.
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Temporarily disable compression
If the layout is correct without compression, the problem is in the assembly, not in your style rules. A quick and reversible test.
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Compare with the default theme
Switching to a standard theme for a few seconds says whether the breakage comes from the theme or elsewhere. Do it outside busy periods.
Carry on with the right page
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Creating a WordPress child theme
How to customise without losing changes at the next update.
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CSS bugs after a PrestaShop theme change
The PrestaShop case, with file compression and overrides.
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Broken navigation menu
If the fault mainly affects the menu, often script-related.
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The child theme explained
Why it exists, and exactly what it protects.
Describe your need in one minute
A few targeted questions so I can reply with an estimate rather than another questionnaire.