How to compile scss to css on npm start

[VishalGulati]

I am unable to compile scss files to css once the application is run using npm start. Is there a way to live reload a sass to css like ts are compiled to js by utility tsc:w. Likewise how can I run gulp watch in sync with npm start or the other way using node-sass on npm start? I tried below approaches but none worked.
Here is the code in package.json:

Using gulp watch:

    "start": "concurrently \"npm run tsc:w\" \"npm run lite\" \"gulp\" ", 
    //also tried gulp watch and that did not work too.
    "start": "concurrently \"npm run tsc:w\" \"npm run lite\" \"gulp watch\" ",

here is my gulppfile.js in the root directory:

    'use strict';
    var gulp = require('gulp');
    var sass = require('gulp-sass');
    gulp.task('sass', function () {
      gulp.src('./sass/**/*.scss')
        .pipe(sass().on('error', sass.logError))
        .pipe(gulp.dest('./css'));
    });
    gulp.task('sass:watch', function () {
      gulp.watch('./sass/**/*.scss', ['sass']);
    });

Using node-sass command:

    "start": "concurrently \"npm run tsc:w\" \"npm run lite\" \"npm run sass\" ",             
    "sass": "node-sass -w app/sass/ -o app/css/",

Could anyone pls tell what I am missing or what is the right way to do it? TIA