[meld/ui-next] filediff: Reinstate grid handle CSS hack

[Kai Willadsen <kaiw src gnome org>]

commit b2e881d1026b2956ab473639665b5c8fd14b8711
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sun Mar 24 07:18:22 2019 +1000

    filediff: Reinstate grid handle CSS hack
    
    Without this, the resize handles drawn by DiffGrid don't display
    correctly.
    
    This was removed in a6d4c07b because I thought the styling was for the
    benefit of the actual notebook background... but it's definitely a
    specific override for DiffGrid.

 data/meld.css                 | 4 ++++
 meld/resources/ui/filediff.ui | 3 +++
 2 files changed, 7 insertions(+)
---
diff --git a/data/meld.css b/data/meld.css
index 10588759..b7bd5bc8 100644
--- a/data/meld.css
+++ b/data/meld.css
@@ -55,6 +55,10 @@ meld-find-bar {
     background-color: @theme_bg_color;
 }
 
+.meld-notebook-child {
+    background-color: @theme_bg_color;
+}
+
 .meld-status-bar {
     border-width: 1px 0 0 0;
     border-style: solid;
diff --git a/meld/resources/ui/filediff.ui b/meld/resources/ui/filediff.ui
index bd067311..8f13a1c9 100644
--- a/meld/resources/ui/filediff.ui
+++ b/meld/resources/ui/filediff.ui
@@ -12,6 +12,9 @@
       <object class="DiffGrid" id="grid">
         <property name="visible">True</property>
         <property name="can_focus">False</property>
+        <style>
+          <class name="meld-notebook-child"/>
+        </style>
         <child>
           <object class="GtkToolbar" id="file_toolbar2">
             <property name="visible">True</property>