UI: support light/dark mode

Change-Id: I99935ebe90c8d674a467e09381976450ce9b3c15
diff --git a/ui/Base.lproj/AccSipGeneral.xib b/ui/Base.lproj/AccSipGeneral.xib
index 1126adb..bfb6ec6 100644
--- a/ui/Base.lproj/AccSipGeneral.xib
+++ b/ui/Base.lproj/AccSipGeneral.xib
@@ -2,6 +2,7 @@
 <document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="14313.18" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
     <dependencies>
         <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="14313.18"/>
+        <capability name="System colors introduced in macOS 10.14" minToolsVersion="10.0"/>
         <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
     </dependencies>
     <objects>
@@ -32,8 +33,8 @@
                         <rect key="frame" x="1" y="1" width="618" height="450"/>
                         <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
                     </view>
-                    <color key="borderColor" red="0.88235294117647056" green="0.88235294117647056" blue="0.88235294117647056" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
-                    <color key="fillColor" red="0.91764705882352937" green="0.91764705882352937" blue="0.91764705882352937" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
+                    <color key="borderColor" name="unemphasizedSelectedTextBackgroundColor" catalog="System" colorSpace="catalog"/>
+                    <color key="fillColor" name="windowBackgroundColor" catalog="System" colorSpace="catalog"/>
                 </box>
                 <view translatesAutoresizingMaskIntoConstraints="NO" id="pL7-7S-saC">
                     <rect key="frame" x="110" y="0.0" width="400" height="513"/>