refactor(scss): remove helper/shadow. Expose shadow style in CSS variables

assets/scss/style.scss

@@ -1,7 +1,5 @@
 @import "breakpoints.scss";
-
 @import "variables.scss";
-@import "helper/shadow.scss";
 
 @import "external/normalize.scss";
 
@@ -112,8 +110,8 @@ main.main {
     padding: 15px 20px;
     border-radius: var(--card-border-radius);
     line-height: 1.75;
-    @include box_shadow(2);
     color: var(--card-text-color-secondary);
+    box-shadow: var(--shadow-l2);
 
     @media (max-width: $on-phone) {
         max-width: 100vw;