fix: init Stylelint for CSS (#472)

* added stylelint for css

* added style:lint to pck.json and edited conflicting files

* added unknown-units rule and edited corresponding file

Author: hertweckhr1

.stylelintrc.yml

@@ -0,0 +1,30 @@
+  rules:
+    block-closing-brace-empty-line-before: never
+    block-no-empty: true
+    block-opening-brace-space-before: always
+    color-no-invalid-hex: true
+    declaration-bang-space-before: always
+    declaration-block-trailing-semicolon: always
+    declaration-colon-space-after: always
+    declaration-colon-space-before: never
+    declaration-property-value-blacklist: [ { '/^outline$/': 'none' }]
+    font-family-no-duplicate-names: true
+    indentation: 4
+    keyframe-declaration-no-important: true
+    length-zero-no-unit: true
+    max-empty-lines: 2
+    no-duplicate-selectors: true
+    no-empty-source: true
+    no-eol-whitespace: true
+    no-extra-semicolons: true
+    number-leading-zero: always
+    number-no-trailing-zeros: true
+    property-case: lower
+    selector-list-comma-space-after: always-single-line
+    selector-list-comma-space-before: never
+    selector-pseudo-class-no-unknown: true
+    selector-pseudo-element-case: lower
+    selector-pseudo-element-colon-notation: single
+    string-no-newline: true
+    unit-case: lower
+    unit-no-unknown: true