Why doesn't autoprefixer work?

Question

gulp.js

Please help me understand, there are no errors, just prefixes are not added...

"use strict";

var gulp = require("gulp");
var pug = require("gulp-pug");
var plumber = require("gulp plumber");
var sourcemaps = require("gulp-sourcemaps");
var rename = require("gulp-rename");
var server = require("browser-sync").create();
var sass = require("gulp-sass");
var postcss = require("gulp-postcss");
var autoprefixer = require("autoprefixer");
var csso = require("gulp-csso");
var imagemin = require("gulp-imagemin");
var posthtml = require("gulp-posthtml");
var include = require("posthtml-include");
var del = require("del");
var htmlmin = require('gulp-htmlmin');
var uglify = require('gulp-uglify-es').default;

// ---------

gulp.task("css", function () {
return gulp.src("src/scss/main.scss")
.pipe(plumber())
.pipe(sourcemaps. init())
.pipe(sass())
.pipe(postcss([
autoprefixer()
]))
.pipe(csso())
.pipe(rename("main.min.css"))
.pipe(sourcemaps.write (""."))
.pipe(gulp.dest("build/css"));
});

// ----------

gulp.task("build", gulp.series("clean", "fonts", "images", "css",
gulp.task("start", gulp.series("build", "server"));