Enhance TopUpModal styling and update localization files

- Updated button styles in TopUpModal for improved visual feedback during interactions.
- Adjusted modal positioning for better user experience on desktop.
- Added 'paymentMethod' key to localization files for English, Persian, Russian, and Chinese languages, enhancing multi-language support.

src/locales/en.json

@@ -254,6 +254,7 @@
     "topUp": "Top Up",
     "topUpBalance": "Top Up Balance",
     "enterAmount": "Enter amount",
+    "paymentMethod": "Payment Method",
     "paymentMethods": "Payment Methods",
     "transactionHistory": "Transaction History",
     "noTransactions": "No transactions",