When the styles do not load, a site turns into a list of text and images with no layout. All the content is intact, the browser simply has no instructions on how it should look. So the fault is in one file or its address, not in the content.
Open the site in a private window and on another device. If the design is fine there, this is your browser cache rather than the site. Clear the cache and the situation resolves.
The browser developer tools have a tab that lists every file the page loads. If the stylesheet row is red with code 404, the file is not at the address the page points to. If the code is 403, the file is there but the server refuses to serve it, see our guide on 403 Forbidden.
Performance plugins combine and minify stylesheets into one. If the combining is interrupted or one file is invalid, the whole bundle breaks. Turn off combining and minification in the plugin, clear the cache and reload. If the design returns, you have found the cause and the settings can be enabled one at a time.
After a migration the database can still hold old addresses, so the site fetches stylesheets from the previous server or the old domain. The developer tools show this immediately, because the file address carries the wrong name. Addresses must be corrected in the database, not by search and replace in files.
If the page loads over an encrypted connection while the stylesheet is requested unencrypted, the browser blocks it and the design disappears. That is a symptom of its own, covered in our guide on the mixed content warning.
Then this is rarely a missing file and more often a theme update that renamed classes or removed customisations. If the changes were made directly to the theme rather than to a child theme, every update wipes them.
Do not start editing theme files before you know whether this is a loading error or missing code. A fix made in the wrong place stays on the site for years. Take a backup before changes, see our guide on backing up a site.
We work out whether the stylesheet fails to load or is broken, and fix the right place. We also make sure the same does not return after the next update or cache purge.
