Fix story caption protection.

app/src/main/res/drawable/story_gradient_bottom.xml

@@ -4,6 +4,6 @@
 
     <gradient android:type="linear"
         android:angle="90"
-        android:startColor="@color/transparent_black_25" />
+        android:startColor="@color/story_caption_gradient_start" />
 
 </shape>

app/src/main/res/values/colors.xml

@@ -7,6 +7,8 @@
 
     <color name="effectively_transparent_black">#01000000</color>
 
+    <color name="story_caption_gradient_start">#8F121212</color>
+
     <color name="transparent_black_05">#0D000000</color>
     <color name="transparent_black_08">#14000000</color>
     <color name="transparent_black_10">#18000000</color>