refactor: extract shared logic to active note state

app/assets/stylesheets/_sn.scss

@@ -162,6 +162,10 @@
   line-height: 2.25rem;
 }
 
+.w-0 {
+  width: 0;
+}
+
 .w-3\.5 {
   width: 0.875rem;
 }
@@ -190,6 +194,10 @@
   height: 1px;
 }
 
+.h-0 {
+  height: 0;
+}
+
 .h-3\.5 {
   height: 0.875rem;
 }