Make header back arrow function for auto save

components/header/symptom-view.js

@@ -2,7 +2,8 @@ import React from 'react'
 import {
   View,
   Text,
-  TouchableOpacity
+  TouchableOpacity,
+  Dimensions
 } from 'react-native'
 import styles, { iconStyles } from '../../styles'
 import FeatherIcon from 'react-native-vector-icons/Feather'
@@ -10,11 +11,12 @@ import NavigationArrow from './navigation-arrow'
 import formatDate from '../helpers/format-date'
 
 export default function SymptomViewHeader(props) {
+  const middle = Dimensions.get('window').width / 2
   return (
     <View style={[styles.header, styles.headerCycleDay, styles.headerSymptom]}>
       <View
         style={styles.accentCircle}
-        left={props.middle - styles.accentCircle.width / 2}
+        left={middle - styles.accentCircle.width / 2}
       />
       <NavigationArrow
         direction='left'