title: how to create circle shape in react native with flex box
body: <p>this is my component:</p>
  
  <pre><code>const styles = {
   menuContainer: {
    flex: 1,
    flexDirection: 'column'  
   },
   menuItem: {
    flex: 1,
    borderRadius: ??
   }
  }
          &lt;View style={styles.menuContainer}&gt;
              &lt;TouchableOpacity {styles.menuItem}/&gt;                    
              &lt;TouchableOpacity {styles.menuItem}/&gt; 
          &lt;/View&gt;
  </code></pre>
  
  <p>bordeRadius in react native doesn't work with percentage like <em>50%</em> and in flex box i don't know the width of each flexItem. do you have any idea without calculate width of each flexItem?</p>