My site is just a grey screen. What is the problem?

If your site is just a grey screen the problem could be due to custom translation edits.

The translation files use JSON. If you have incorrect JSON format in any of your translation files then the site will show up as grey because the site can’t parse the JSON so it gives an error.
For example in this image the JSON file is missing a comma:

This causes the site to look like this:

That means your JSON isn’t correct and has errors. Check your translation files to make sure there are no JSON errors. While editting your JSON you can use a code editor like vscode which will alert you when your file has a JSON error. You can also use a service like https://jsonlint.com/ to validate your JSON.

Once all JSON errors are solved then your site will no longer be grey.