restore css about grw-three-stranded-button

src/client/styles/scss/theme/_apply-colors-dark.scss

@@ -228,6 +228,15 @@ ul.pagination {
   background-color: rgba($bgcolor-subnav, 0.85);
 }
 
+.grw-three-stranded-button {
+  .btn-outline-primary {
+    &:hover {
+      color: $primary;
+      background-color: $gray-700;
+    }
+  }
+}
+
 // Search drop down
 #search-typeahead-asynctypeahead {
   background-color: $bgcolor-global;

src/client/styles/scss/theme/_apply-colors-light.scss

@@ -144,6 +144,15 @@ $table-hover-bg: $bgcolor-table-hover;
   background-color: rgba($bgcolor-subnav, 0.85);
 }
 
+.grw-three-stranded-button {
+  .btn-outline-primary {
+    &:hover {
+      color: $primary;
+      background-color: $gray-200;
+    }
+  }
+}
+
 .grw-drawer-toggler {
   @extend .btn-light;
   color: $gray-500;