Replace $white with a color working in both themes #13425

public/sass/components/_form_select_box.scss

@@ -87,7 +87,7 @@ $select-input-bg-disabled: $input-bg-disabled;
 }
 
 .gf-form-select2__select-arrow {
-  border-color: $white transparent transparent;
+  border-color: $input-color-select-arrow transparent transparent;
   border-style: solid;
   border-width: 5px 5px 2.5px;
   display: inline-block;
@@ -96,7 +96,7 @@ $select-input-bg-disabled: $input-bg-disabled;
   position: relative;
 
   &.gf-form-select2__select-arrow--reversed {
-    border-color: transparent transparent $white;
+    border-color: transparent transparent $input-color-select-arrow;
     top: -2px;
     border-width: 0 5px 5px;
   }