Implement CheckmarkPopup

uhabits-android/src/main/res/drawable/checkmark_dialog_bg.xml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="utf-8"?><!--
+  ~ Copyright (C) 2016-2021 Álinson Santos Xavier <git@axavier.org>
+  ~
+  ~ This file is part of Loop Habit Tracker.
+  ~
+  ~ Loop Habit Tracker is free software: you can redistribute it and/or modify
+  ~ it under the terms of the GNU General Public License as published by the
+  ~ Free Software Foundation, either version 3 of the License, or (at your
+  ~ option) any later version.
+  ~
+  ~ Loop Habit Tracker is distributed in the hope that it will be useful, but
+  ~ WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+  ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+  ~ more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License along
+  ~ with this program. If not, see <http://www.gnu.org/licenses/>.
+  -->
+
+<shape xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shape="rectangle">
+    <solid android:color="?attr/contrast0" />
+    <stroke
+        android:width="2dp"
+        android:color="?contrast40" />
+    <corners android:radius="5dp" />
+</shape>