What should I do to make postcss (posthtml) work in Gulp?

Question

gulp.js

Can't figure out what to do to make postcss (posthtml) work in Gulp:
Could not find a declaration file for module 'gulp-postcss'. '/Users/1ego/Documents/projects/skinali/node_modules/gulp-postcss/index.js' implicitly has an 'any' type. Try npm install @types/gulp-postcss if it exists or add a new declaration (.d.ts) file containing declare module 'gulp-postcss';
npm ERR! A complete log of this run can be found in: npm ERR! /Users/1ego/.npm/_logs/2019-04-08T14_26_28_651Z-debug.log
What is this error? What to do? How to avoid in the future? What and, most importantly, where to look, what would be corrected?