declare module 'csso-webpack-plugin' {
    declare type PluginOptions = any;
    declare type PluginFilterFn = (file: string) => boolean;
    declare type PluginFilter = PluginFilterFn | RegExp;

    declare export default class CssoWebpackPlugin {
        constructor(options?: PluginOptions, filter?: PluginFilter): this;
        apply(compiler: Compiler): void
    }
}