I'm starting a new project with angular 4, and I want to integrate with PostCss for use modules such as: Autoprefixer, CSSNext and another modules.
you can try this way https://github.com/angular/angular-cli/issues/1512#issuecomment-254262959 But I need say what I don't used it before.
And if you don't use CLI, then may try set options in webpack config for build css code from scss, for example. Just use require() for your styling file. Read more here (in notice block) https://angular.io/docs/ts/latest/guide/component-styles.html#!#style-urls-in-metadata