Added theme, reworked UI

lib/pages/data/data_page.dart

@@ -15,24 +15,25 @@ class DataPage extends StatelessWidget {
         ),
         padding: const EdgeInsets.symmetric(vertical: 9, horizontal: 10),
         margin: const EdgeInsets.symmetric(vertical: 2, horizontal: 10),
-        child: const Column(
+        child: Column(
           crossAxisAlignment: CrossAxisAlignment.start,
           children: [
-            Text(
+            const Text(
               'Settings',
               style: TextStyle(
                 fontWeight: FontWeight.w900,
                 fontSize: 35,
               ),
             ),
-            Row(
-              crossAxisAlignment: CrossAxisAlignment.start,
-              children: [
-                ImportSettings(),
-                CategoriesSettings(),
-                AccountSettings(),
-              ],
-            )
+            Expanded(
+              child: ListView(
+                children: const [
+                  ImportSettings(),
+                  CategoriesSettings(),
+                  AccountSettings(),
+                ]
+              )
+            ),
           ]
         )
       )