HTML Error Page served as CSS - Refused to apply style

Question

I have a Spring Boot application, I'm using MVC model. Sometimes when my CSS styles are not loaded for a certain page, I get a strange message in google console: Refused to apply style from 'http://localhost:8080/error_page' because its MIME type ('text/html') is not a supported stylesheet MIME type, and strict MIME checking is enabled.My question is, why app want to apply style from my error_page.html html page? error_page.html is definitely not a CSS file.

My controller method for the error page is very simple:

@RequestMapping(value = "/error_page", method = RequestMethod.GET)
public String homeError(Model model)
{
    return "/error_page";
}