refactor login error message

Signed-off-by: fufesou <shuanglongchen@yeah.net>

flutter/lib/common/widgets/login.dart

@@ -199,22 +199,23 @@ class _WidgetOPState extends State<WidgetOP> {
           return Offstage(
             offstage:
                 _failedMsg.isEmpty && widget.curOP.value != widget.config.op,
-              child: Row(
-                children: [
-                  Text(
-                    _stateMsg,
-                    style: TextStyle(fontSize: 12),
-                  ),
-                  SizedBox(width: 8),
-                  Text(
-                    _failedMsg,
-                    style: TextStyle(
+            child: RichText(
+              text: TextSpan(
+                text: '$_stateMsg  ',
+                style:
+                    DefaultTextStyle.of(context).style.copyWith(fontSize: 12),
+                children: <TextSpan>[
+                  TextSpan(
+                    text: _failedMsg,
+                    style: DefaultTextStyle.of(context).style.copyWith(
                           fontSize: 14,
                           color: Colors.red,
                         ),
                   ),
                 ],
-              ));
+              ),
+            ),
+          );
         }),
         Obx(
           () => Offstage(