I have a problem with CSS and Thymeleaf.
In my Spring boot app, I have this structure:
The main culprit of this behaviour is a custom security configuration which is very likely you are doing in your WebSecurityConfigurerAdapter subclass. If you use SpringBoot 2+ version you should add the following line in your WebSecurityConfigurerAdapter configuration
.requestMatchers(PathRequest.toStaticResources().atCommonLocations()).permitAll()