Gulpfile.js

var gulp = require("gulp");
var sass = require("gulp-sass");
var exec = require("gulp-exec");

gulp.task("styles", function (done) {
  gulp
    .src("gtk-3.0/**/*.scss")
    .pipe(sass().on("error", sass.logError))
    .pipe(gulp.dest("./gtk-3.0/"))
    .pipe(
      exec('gsettings set org.gnome.desktop.interface gtk-theme "Kripton"')
    );
  done();
});

gulp.task("shell-style", function (done) {
  gulp
    .src("gnome-shell/*.scss")
    .pipe(sass().on("error", sass.logError))
    .pipe(gulp.dest("./gnome-shell/"))
    .pipe(
      exec('gsettings set org.gnome.shell.extensions.user-theme name "Kripton"')
    );
  done();
});

//Watch task
gulp.task("default", function () {
  gulp.watch("gtk-3.0/**/*.scss", gulp.series("styles"));
});

gulp.task("shell", function () {
  gulp.watch("gnome-shell/*.scss", gulp.series("shell-style"));
});