This type of error can appear in Divi > Theme Options > Custom CSS box and in Advanced settings of the modules if CSS code has incorrect syntax. Usually the error appear if the closing brace is missing.

Correct CSS rule should look like this

selector {
property_name: property_value;
}

If you see the error you will need to make sure that all CSS rules have opening and closing braces, here is an example

In case you are using @media query make sure that all opening braces have closing braces. Here is an example of valid @media CSS code:

@media (max-width: 980px) { 

selector {
property_name: property_value;
}

}

In Advanced settings of the modules you can add only CSS properties, CSS selector will be added automatically on the front end. Clicking on the help icon will show which selector will be used. Correct CSS syntax in this case will be

property_name: property_value;

Here is an example:

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