Fix Dropdown Item Selection Animation Consistency

src/app/components/dropdown/dropdown.scss

@@ -114,7 +114,7 @@ $dropdown_animation_duration: 0.2s;
   padding: 0 16px;
   position: relative;
   line-height: 1.2; // descender 보호를 위해 1에서 1.2로 수정
-  transition: background-color $dropdown_animation_duration $dropdown_animation_timing;
+  transition: background-color var(--dropdown-duration) $dropdown_animation_timing;
 
   &:hover, &.focused {
     background-color: $dropdown_hover;