title: Android studio is not showing toolbar but device is showing it
body: <p>I'm using </p>
  
  <pre><code>Android Studio 3.1.3
  Build #AI-173.4819257, built on June 4, 2018
  JRE: 1.8.0_152-release-1024-b01 amd64
  JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
  Linux 4.15.0-29-generic
  </code></pre>
  
  <p>with dependencies</p>
  
  <pre><code>implementation 'com.android.support:appcompat-v7:28.0.0-beta01'
  </code></pre>
  
  <p>Here is Toolbar Layout:</p>
  
  <pre><code>&lt;android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:id="@+id/toolbar"
      android:layout_width="match_parent"
      android:layout_height="?attr/actionBarSize"
      android:background="?attr/colorPrimary"
      android:elevation="4dp"
      app:popupTheme="@style/AppTheme.PopupOverlay"
      app:theme="@style/ToolBarStyle" /&gt;
  </code></pre>
  
  <p><strong>Problem:</strong> Android studio is not showing design layout but I can see Toolbar when I run the code.</p>