diff --git a/src/main/res/values/styles.xml b/src/main/res/values/styles.xml
index efa07058..78c52a46 100644
--- a/src/main/res/values/styles.xml
+++ b/src/main/res/values/styles.xml
@@ -18,11 +18,13 @@
         <item name="colorAccent">@color/material_accent_500</item>
         <item name="colorPrimary">@color/material_accent_500</item>
         <item name="colorPrimaryDark">@color/material_accent_700</item>
+        <item name="android:windowBackground">@android:color/transparent</item>
     </style>
     <style name="Theme.Material.Dialog.Alert" parent="Theme.AppCompat.Light.Dialog.Alert">
         <item name="colorAccent">@color/material_accent_500</item>
         <item name="colorPrimary">@color/material_accent_500</item>
         <item name="colorPrimaryDark">@color/material_accent_700</item>
+        <item name="android:windowBackground">@android:color/transparent</item>
     </style>
 
     <style name="PopupTheme" parent="Theme.Material.Dialog">
@@ -35,6 +37,7 @@
         <item name="android:windowActionModeOverlay">true</item>
         <item name="android:colorBackgroundCacheHint">@null</item>
         <item name="android:windowIsTranslucent">true</item>
+        <item name="android:windowBackground">@android:color/transparent</item>
     </style>
 
 </resources>
diff --git a/src/main/scala/com/github/shadowsocks/utils/TrafficMonitor.scala b/src/main/scala/com/github/shadowsocks/utils/TrafficMonitor.scala
index dd055ed0..b762eb2e 100644
--- a/src/main/scala/com/github/shadowsocks/utils/TrafficMonitor.scala
+++ b/src/main/scala/com/github/shadowsocks/utils/TrafficMonitor.scala
@@ -2,7 +2,7 @@ package com.github.shadowsocks.utils
 
 import android.net.TrafficStats
 import android.os.Process
-import java.lang.{String, System}
+import java.lang.{String, System, Math}
 import java.util.Locale
 
 case class Traffic(tx: Long, rx: Long, timestamp: Long)
@@ -20,8 +20,8 @@ object TrafficMonitor {
   var rxTotal: Long = 0
 
   def getTraffic(): Traffic = {
-    new Traffic(TrafficStats.getTotalTxBytes - TrafficStats.getUidTxBytes(uid),
-      TrafficStats.getTotalRxBytes - TrafficStats.getUidRxBytes(uid), System.currentTimeMillis())
+    new Traffic(Math.max(TrafficStats.getTotalTxBytes - TrafficStats.getUidTxBytes(uid), 0),
+      Math.max(TrafficStats.getTotalRxBytes - TrafficStats.getUidRxBytes(uid), 0), System.currentTimeMillis())
   }
 
   def formatTraffic(n: Long): String = {