add the widget base

app/src/main/AndroidManifest.xml

@@ -18,6 +18,19 @@
                 <category android:name="android.intent.category.LAUNCHER"/>
             </intent-filter>
         </activity>
+
+        <receiver
+            android:name=".MyWidgetProvider"
+            android:icon="@mipmap/ic_launcher"
+            android:label="Simple Calendar">
+            <intent-filter>
+                <action android:name="android.appwidget.action.APPWIDGET_UPDATE"/>
+            </intent-filter>
+
+            <meta-data
+                android:name="android.appwidget.provider"
+                android:resource="@xml/widget_info"/>
+        </receiver>
     </application>
 
 </manifest>

app/src/main/java/calendar/simplemobiletools/com/MyWidgetProvider.java

@@ -0,0 +1,13 @@
+package calendar.simplemobiletools.com;
+
+import android.appwidget.AppWidgetManager;
+import android.appwidget.AppWidgetProvider;
+import android.content.Context;
+
+public class MyWidgetProvider extends AppWidgetProvider {
+
+    @Override
+    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
+
+    }
+}

app/src/main/res/values/styles.xml

@@ -8,7 +8,7 @@
         <item name="colorAccent">@color/colorAccent</item>
     </style>
 
-    <style name="dayView" parent="AppTheme">
+    <style name="dayView">
         <item name="android:gravity">center</item>
         <item name="android:textColor">@color/lightGrey</item>
         <item name="android:textSize">@dimen/day_text_size</item>

app/src/main/res/xml/widget_info.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
+                    android:initialLayout="@layout/activity_main"
+                    android:minHeight="250dp"
+                    android:minWidth="250dp">
+</appwidget-provider>