Add --silence-deprecation flag

Author: pastelcyborg

package.json

@@ -30,8 +30,8 @@
     "start": "yarn build && yarn serve",
     "build": "yarn build-scss && yarn build-js && yarn build-class-references",
     "build-tokens": "((style-dictionary build --verbose --config ./sd.config.json) || true)",
-    "build-scss": "yarn build-tokens && sass --load-path=node_modules --embed-sources --style=compressed scss:build/css && postcss --use autoprefixer --replace 'build/css/**/*.css' --map",
-    "build:essential": "yarn run build-js && sass --load-path=node_modules --embed-sources --style=compressed scss/build.scss:build/css/build.css scss/docs:build/css/docs && postcss --use autoprefixer --replace 'build/css/**/*.css' --map",
+    "build-scss": "yarn build-tokens && sass --load-path=node_modules --embed-sources --style=compressed --silence-deprecation=mixed-decls scss:build/css && postcss --use autoprefixer --replace 'build/css/**/*.css' --map",
+    "build:essential": "yarn run build-js && sass --load-path=node_modules --embed-sources --style=compressed --silence-deprecation=mixed-decls scss/build.scss:build/css/build.css scss/docs:build/css/docs && postcss --use autoprefixer --replace 'build/css/**/*.css' --map",
     "build-js": "mkdir -p build/js/modules && cp node_modules/@canonical/cookie-policy/build/js/cookie-policy.js build/js/modules && cp node_modules/@canonical/latest-news/dist/latest-news.js build/js/modules && cp node_modules/js-beautify/js/lib/beautify.js node_modules/js-beautify/js/lib/beautify-html.js node_modules/js-beautify/js/lib/beautify-css.js build/js/modules",
     "build-class-references": "node scripts/create-class-references.js",
     "cypress:open": "cypress open",
@@ -42,8 +42,8 @@
     "test": "yarn lint-scss && yarn lint-prettier &&  yarn test-spelling && yarn test-scss && yarn jest",
     "lint-prettier": "prettier -c .",
     "lint-scss": "stylelint 'scss/**/*.scss'",
-    "watch:scss": "sass --load-path=node_modules --embed-sources --style=compressed scss:build/css --watch",
-    "watch:essential": "sass --load-path=node_modules --embed-sources --style=compressed scss/build.scss:build/css/build.css --watch",
+    "watch:scss": "sass --load-path=node_modules --embed-sources --style=compressed --silence-deprecation=mixed-decls scss:build/css --watch",
+    "watch:essential": "sass --load-path=node_modules --embed-sources --style=compressed --silence-deprecation=mixed-decls scss/build.scss:build/css/build.css --watch",
     "watch": "yarn build && yarn watch:scss",
     "clean": "rm -rf build docs/static/css node_modules/ yarn-error.log",
     "percy": "percy snapshot snapshots.js",