Added Background Gradient for Signup Page

Author: Jack

lib/const/gradient_const.dart

@@ -0,0 +1,13 @@
+import 'package:flutter/material.dart';
+import 'color_const.dart';
+
+const LinearGradient SIGNUP_BACKGROUND = LinearGradient(
+    begin: FractionalOffset(0.0, 0.4),
+    end: FractionalOffset(0.9, 0.7),
+    // Add one stop for each color. Stops should increase from 0 to 1
+    stops: [0.1, 0.9],
+    colors: [
+      YELLOW,
+      BLUE
+    ]
+);

lib/page/signup/SignPageOne.dart

@@ -4,6 +4,8 @@
 /// Email: niebin312@gmail.com
 ///
 import "package:flutter/material.dart";
+import '../../const/color_const.dart';
+import '../../const/gradient_const.dart';
 
 class SignPageOne extends StatefulWidget {
   @override
@@ -14,10 +16,14 @@ class _SignOneState extends State<SignPageOne> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(
-        title: Text("Sign up one"),
+      body: Container(
+        decoration: BoxDecoration(
+          gradient: SIGNUP_BACKGROUND
+        ),
+        child: Center(
+          child: Text("Start"),
+        ),
       ),
-      body: Text("Sign up page one"),
     );
   }
 }