it violates the following Content Security Policy directive: "default-src ". Note that 'script-src-elem' was not explicitly set, so 'default-src' is used as a fallback. code example

Example: because it violates the following Content Security Policy directive: "default-src 'none'". Note that 'font-src' was not explicitly set, so 'default-src' is used as a fallback

devServer: {

        historyApiFallback: true
    }
};