Update brightness slider thumb and spacing

Also fixes a few errors in the measuring logic.

Bug: 15170399
Change-Id: I7ce7edef0a08dc00ef747988cd64e40a9fbae192
diff --git a/packages/SystemUI/AndroidManifest.xml b/packages/SystemUI/AndroidManifest.xml
index e48aef1..b8836a0 100644
--- a/packages/SystemUI/AndroidManifest.xml
+++ b/packages/SystemUI/AndroidManifest.xml
@@ -327,7 +327,7 @@
         <activity
             android:name=".settings.BrightnessDialog"
             android:label="@string/quick_settings_brightness_dialog_title"
-            android:theme="@android:style/Theme.DeviceDefault.Light.Dialog"
+            android:theme="@android:style/Theme.DeviceDefault.Dialog"
             android:finishOnCloseSystemDialogs="true"
             android:launchMode="singleInstance"
             android:excludeFromRecents="true"