InterstitialAd Admob not visible

If on Android emulator home button pressed.

// button home presssed
19:37:06.727: INFO/ActivityManager(60): Starting: 
Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] 
flg=0x10200000 cmp=com.android.launcher/com.android.launcher2.Launcher } from pid 60

19:37:06.807: INFO/onSaveInstanceState(339): onSaveInstanceState()
19:37:06.848: INFO/onPause(339): onPause()
19:37:07.968: INFO/onStop(339): onStop()

Diagram of Activity lifecycle if button HOME pressed

How set rounded corners and own styles ActivityMy.java

Button btn.setBackgroundResource(R.drawable.back_button_answer);

\res\drawable\back_button_answer.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="//schemas.android.com/apk/res/android" android:shape="rectangle" >
   <corners android:radius="10dip" />
   <!-- background -->
   
   <gradient
                android:startColor="#D6D7D6"
                android:centerColor="#E2E2E2"
                android:centerY="0.75"
                android:endColor="#D6D7D6"
                android:angle="270"
        />
   
   <stroke android:width="2dip" android:color="#fff"/>
</shape>

If the app have transparent menu and you do not want this,
try delete @style/AppTheme in application tag in AndroidManifest.xml
and try run module - project. If menu is not transparent , maybe it caused

 <application
        android:allowBackup="true"
        android:icon="@drawable/dicts_ico"
        android:label="@string/app_name" 
        android:theme="@style/AppTheme" // delete this row - run app - try menu
 >

Or try set values\styles.xml into basic Theme

<resources>

    <!--
        Base application theme, dependent on API level. This theme is replaced
        by AppBaseTheme from res/values-vXX/styles.xml on newer devices.
    -->
    <style name="AppBaseTheme" parent="android:Theme.Black">
        <!--
            Theme customizations available in newer API levels can go in
            res/values-vXX/styles.xml, while customizations related to
            backward-compatibility can go here.
        -->
    </style>

    <!-- Application theme. -->
    <style name="AppTheme" parent="AppBaseTheme">
        <!-- All customizations that are NOT specific to a particular API-level can go here. -->
    </style>

</resources>

build.gradle in module have higher priority then AndrodiManifest.xml
Try this.
AndroidManifest.xml have code:

    <uses-sdk
        android:minSdkVersion="9"
        android:targetSdkVersion="23" />

build.gradle have code:

   defaultConfig {
        applicationId "cz.okhelp.words"
        minSdkVersion 9
        targetSdkVersion 19
        versionCode 107
        versionName "1.0.7"
    }

Warning in AndroidManifest.xml:
This targetSdkVersion value (23) is not used; it is always overridden by the value specified in the Gradle build script (19) less... (Ctrl+F1)
The value of (for example) minSdkVersion is only used if it is not specified in the build.gradle build scripts. When specified in the Gradle build scripts, the manifest value is ignored and can be misleading, so should be removed to avoid ambiguity.

Android Emulator warning:[Accessibility] Missing contentDescription attribute on image

Workaround example code:

android:contentDescription="@string/desc"

            <ImageView
                android:id="@+id/imageViewOil"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
            android:contentDescription="@string/desc"
                android:layout_alignParentLeft="true"
                android:layout_centerVertical="true"
                android:layout_marginLeft="84dp"
                android:src="@drawable/tank_silver" />