simplify style file content

[cooljser]

[terence55]

Could you provide a reproducible demo in codesandbox or codepen for this issue? Simplifications are made when using less-loader or sass-loader. This issue may occur when using only css-loader, but the PR implementation is intrusive as this plugin is only used for code generation and not code modification. To simplify the code, we can use optimize-css-assets-webpack-plugin for Webpack v4 or css-minimizer-webpack-plugin for Webpack v5.