feat: add stylelint

frontend/app/src/theme/common/_helper.scss

@@ -41,6 +41,7 @@
     li img {
       max-height: 1.25rem;
       vertical-align: text-bottom;
+
       // filter: invert(45%) sepia(0%) saturate(0%) hue-rotate(227deg) brightness(97%) contrast(82%);
     }
   }
@@ -48,11 +49,13 @@
 
 %horizontal-list {
   @extend %vertical-list;
+
   ul {
     li {
       display: inline;
     }
-    li:not(:first-child):before {
+
+    li:not(:first-child)::before {
       content: ' • ';
     }
   }
@@ -64,6 +67,7 @@
 
 .horizontal-list {
   @extend %vertical-list;
+
   li {
     display: inline;
   }