Introduce item-list CSS, move item colors to variables

app/styles/components/_contribution-list.scss

@@ -31,15 +31,8 @@ ul.contribution-list {
     grid-template-columns: auto 5rem 5rem;
     grid-row-gap: 0.5rem;
     padding: 0.8rem 1.2rem;
-    background-color: rgba(255,255,255,0.1);
-    font-size: 1.2rem;
-    border-bottom: 1px solid rgba(255,255,255,0.2);
     cursor: pointer;
 
-    &:first-of-type {
-      border-top: 1px solid rgba(255,255,255,0.2);
-    }
-
     &.confirmed {
       grid-template-columns: auto 5rem;
     }
@@ -50,10 +43,6 @@ ul.contribution-list {
       opacity: 0.6;
     }
 
-    &.selected {
-      background-color: rgba(255,255,255,0.2);
-    }
-
     p {
       align-self: center;
       margin: 0;
@@ -113,14 +102,4 @@ ul.contribution-list {
       margin-right: 0.5rem;
     }
   }
-
-  &.loading {
-    @include loading-border-top;
-
-    li {
-      &:first-of-type {
-        border-top: none;
-      }
-    }
-  }
 }