关闭背景时亮度可调

新增自定义图片背景功能（可调透明度，目前仅电脑可用）

parts/language/lang_en.lua

@@ -138,6 +138,7 @@ return{
     chatHistory="------New messages below------",
 
     keySettingInstruction="Press to bind key\nescape: cancel\nbackspace: delete",
+    customBGhelp="Drop image file here to apply custom background",
 
     errorMsg="Techmino ran into a problem and needs to restart.\nYou can send the error log to the developers.",
     tryAnotherBuild="[Invalid UTF-8] If you are on Windows, try downloading Techmino-win32 or Techmino-win64 (different from what you are using now).",
@@ -390,7 +391,10 @@ return{
             power="Battery Info",
             clean="Quick Draw",
             fullscreen="Fullscreen",
-            bg="Background",
+
+            bg_on="Normal Backgrounds",
+            bg_off="No Background",
+            bg_custom="Apply Custom BG",
 
             blockSatur="Block Saturation",
             fieldSatur="Field Saturation",