welcome: added scrollbar to privacy policy

lib/widgets/welcome_page.dart

@@ -157,15 +157,27 @@ class _WelcomePageState extends State<WelcomePage> {
       constraints: BoxConstraints(maxWidth: 460),
       child: ClipRRect(
         borderRadius: BorderRadius.circular(16),
-        child: Markdown(
+        child: Theme(
-          data: terms,
+          data: Theme.of(context).copyWith(
-          selectable: true,
+            scrollbarTheme: ScrollbarThemeData(
-          onTapLink: (text, href, title) async {
+              radius: Radius.circular(16),
-            if (await canLaunch(href)) {
+              crossAxisMargin: 6,
-              await launch(href);
+              mainAxisMargin: 16,
-            }
+              interactive: true,
-          },
+            ),
-          shrinkWrap: true,
+          ),
+          child: Scrollbar(
+            child: Markdown(
+              data: terms,
+              selectable: true,
+              onTapLink: (text, href, title) async {
+                if (await canLaunch(href)) {
+                  await launch(href);
+                }
+              },
+              shrinkWrap: true,
+            ),
+          ),
         ),
       ),
     );