Is there a complete tutorial on how to compile modified css

Here is another tutorial explaining sass bundling and package imports: https://mdbootstrap.com/learn/mdb-foundations/mdb-advanced-features/sass-scss/

And here is a tutorial that can help you with webpack configuration: https://mdbootstrap.com/docs/standard/getting-started/webpack-integration/

Some parts will be different but Installation and part of To Do App with MDB can be useful for you:

https://mdbootstrap.com/docs/standard/integrations/aspnet/

There is no need to use webpack as you can simply invoke the SASS compiler with a gulp script.

It takes any .scss script from the ./Styles directory and also builds the two MDB css files.

const gulp = require("gulp");
const sass = require("gulp-sass")(require("sass"));
const rename = require("gulp-rename");
const cleanCSS = require("gulp-clean-css");
const sourcemaps = require("gulp-sourcemaps");

const scssSources = [
    "./Styles/*.scss",
    "./wwwroot/mdb/src/mdb/scss/mdb.pro.scss",
    "./wwwroot/mdb/src/mdb/scss/mdb.dark.scss",
    "./wwwroot/mdb/src/mdb/scss/bootstrap/bootstrap.scss"
]

const plain_css = (cb) =>
{
    gulp.src(scssSources)
        .pipe(sourcemaps.init())
        .pipe(sass())
        .pipe(sourcemaps.write())
        .pipe(gulp.dest("./wwwroot/css/"));
    cb();
}

const min_css = (cb) => 
{
    gulp.src(scssSources)
        .pipe(rename({ extname: ".min.css" }))
        .pipe(sourcemaps.init())
        .pipe(sass())
        .pipe(cleanCSS())
        .pipe(sourcemaps.write())
        .pipe(gulp.dest("./wwwroot/css/"));
    cb();
}

gulp.task("sass", gulp.parallel(plain_css, min_css));

gulp.task("default", function() {
   return gulp.watch("./Styles/*.scss", gulp.parallel(plain_css, min_css));
});

Then you can add it to you package.json compile-sass in the scripts section as below:

{
  "version": "1.0.0",
  "name": "test-project",
  "private": true,
  "scripts": {
    "compile-sass": "gulp sass"
  },
  "devDependencies": {
    "gulp": "^4.0.2",
    "gulp-clean-css": "^4.3.0",
    "gulp-rename": "^2.0.0",
    "gulp-sass": "^5.1.0",
    "gulp-sourcemaps": "^3.0.0",
    "sass": "^1.58.3"
  }
}

Then you can either call npm run compile-sass from the command line of add it as a target in you project file as below:

  <!-- Make sure NPM is installed & restore packages before build -->
  <Target Name="EnsureNodeEnv" BeforeTargets="Build">
    <Exec Command="node --version" ContinueOnError="true">
      <Output TaskParameter="ExitCode" PropertyName="ErrorCode" />
    </Exec>
    <Error Condition="'$(ErrorCode)' != '0'" Text="Node.js is required to build and run this project. To continue, please install Node.js from https://nodejs.org/, and then restart your command prompt or IDE." />
    <Message Importance="high" Text="Restoring dependencies using 'npm'. This may take several minutes..." />
    <Exec WorkingDirectory="$(ProjectDir)" Command="npm install -s --no-audit" />
  </Target>
  <!-- Compile SASS to CSS -->
  <Target Name="GulpCompileSass" AfterTargets="EnsureNodeEnv">
    <Message Importance="high" Text="Compiling SASS, this may take several minutes..." />
    <Exec Command="npm run compile-sass -s" ContinueOnError="false">
      <Output TaskParameter="ExitCode" PropertyName="ErrorCode" />
    </Exec>
    <Error Condition="'$(ErrorCode)' != '0'" Text="Failed to compile SASS." />
  </Target>