Install and setup stylelint

.stylelintrc.json

@@ -0,0 +1,29 @@
+{
+  "extends": [
+    "stylelint-config-standard-scss"
+  ],
+  "plugins": [
+    "stylelint-scss"
+  ],
+  "rules": {
+    "scss/at-import-partial-extension": null,
+    "scss/at-rule-no-unknown": true,
+    "at-rule-no-unknown": null,
+    "color-hex-length": "long",
+    "color-hex-case": "upper",
+    "comment-whitespace-inside": null,
+    "declaration-block-no-duplicate-properties": true,
+    "function-name-case": null,
+    "max-empty-lines": 2,
+    "number-leading-zero": "always",
+    "no-descending-specificity": null,
+    "no-duplicate-at-import-rules": true,
+    "rule-empty-line-before": ["always-multi-line", {"ignore": ["after-comment"]}],
+    "shorthand-property-no-redundant-values": [true, {"severity": "warning"}],
+    "selector-class-pattern": null,
+    "selector-id-pattern": null,
+    "selector-max-id": 1,
+    "string-quotes": "double",
+    "value-keyword-case": "lower"
+  }
+}

package.json

@@ -2,6 +2,7 @@
   "scripts": {
     "lint": "yarn run eslint --ext .ts app/javascript",
     "lint:fix": "yarn run eslint --ext .ts app/javascript --fix",
+    "lint:css": "yarn run stylelint \"app/assets/stylesheets/**/*.scss\"",
     "build": "esbuild app/javascript/*.* --bundle --sourcemap --outdir=app/assets/builds --public-path=assets",
     "build:css": "sass ./app/assets/stylesheets/application.sass.scss:./app/assets/builds/application.css --no-source-map --load-path=node_modules"
   },
@@ -28,6 +29,9 @@
     "@typescript-eslint/parser": "^4.11.0",
     "esbuild": "^0.17.0",
     "eslint": "^7.16.0",
-    "eslint-plugin-import": "^2.27.4"
+    "eslint-plugin-import": "^2.27.4",
+    "stylelint": "^14.16.1",
+    "stylelint-config-standard-scss": "^6.1.0",
+    "stylelint-scss": "^4.3.0"
   }
 }