refactor: convert legacy color classes to tailwind syntax

Replace all custom `bg-*` utility classes across Vue components with Tailwind's arbitrary hex color notation (e.g. `bg-[#f7f7f7]`). Remove redundant hardcoded background color definitions from src/static/scss/background.scss, clean up template formatting, and update gradient button styles to use direct hex values.

src/pages-order/order/components/FooterSection/index.vue

@@ -8,7 +8,7 @@
     <button :class="[
       'right border-none rounded-10 flex flex-full flex-items-center flex-justify-center font-size-14 font-500 bg-theme-color-500',
       {
-        'bg-FF3D60': statusCode === '0',
+        'bg-[#ff3d60]': statusCode === '0',
         'color-white': ['1', '2', '3', '4', '5', '6'].includes(statusCode),
       },
     ]" @click="handleButtonClick(orderData)">