Package.json -> Scripts. To generate a source map, use --source-map

.gitignore

@@ -11,3 +11,4 @@ ad.js
 TODO
 test.html
 .vscode/
+.vs/

package.json

@@ -9,7 +9,7 @@
     "css": "npm-run-all --sequential css-compile css-prefix css-minify",
     "css-compile": "node-sass --output-style expanded --source-map true --source-map-contents true --precision 6 build/scss/AdminLTE.scss dist/css/adminlte.css",
     "css-prefix": "postcss --config build/config/postcss.config.js --replace \"dist/css/*.css\" \"!dist/css/*.min.css\"",
-    "css-minify": "cleancss --level 1 --source-map dist/css/adminlte.css.map --output dist/css/adminlte.min.css dist/css/adminlte.css",
+    "css-minify": "cleancss --level 1 --source-map --output dist/css/adminlte.min.css dist/css/adminlte.css",
     "compile": "npm-run-all --parallel js css",
     "dev": "npm-run-all --parallel watch sync",
     "js": "npm-run-all --sequential js-compile js-minify",