[gnome-software] css: gtk+3.18 friendly style

[Lapo Calamandrei <lapo src gnome org>]

commit 7e7510c7c64a85fd8a0ccb73bb8c1ed2b0da41e6
Author: Lapo Calamandrei <calamandrei gmail com>
Date:   Thu Jun 30 18:04:35 2016 +0200

    css: gtk+3.18 friendly style
    
    use old style selectors when it makes sense and replace the image()
    used for the separator with a solid linear gradient since it makes
    gnome-software crash otherwise.

 src/gtk-style.css |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)
---
diff --git a/src/gtk-style.css b/src/gtk-style.css
index 72d1f79..7e103af 100644
--- a/src/gtk-style.css
+++ b/src/gtk-style.css
@@ -185,8 +185,9 @@
        all: unset;
 }
 
-.review-row button { font-size: smaller; }
+.review-row button, .review-row .button { font-size: smaller; }
 
+/* gtk+ 3.20+ only +/
 .review-row .vote-buttons button {
        margin-right: -1px;
 
@@ -194,12 +195,12 @@
        transition-property: background, box-shadow, border-style, text-shadow;
 }
 
-/* this is the separator between yes and no vote buttons */
+/* this is the separator between yes and no vote buttons, gtk+ 3.20 only */
 .review-row .vote-buttons button:not(:first-child):not(:hover):not(:active):not(:backdrop) {
-       border-image: image(@borders) 0 0 0 1 / 5px 0 5px 1px;
+       border-image: linear-gradient(to top, @borders, @borders) 0 0 0 1 / 5px 0 5px 1px;
 }
   .review-row .vote-buttons button:not(:first-child):backdrop {
-       border-image: image(@unfocused_borders) 0 0 0 1 / 5px 0 5px 1px;
+       border-image: linear-gradent(to top, @unfocused_borders, @unfocused_border) 0 0 0 1 / 5px 0 5px 1px;
   }
 
 .reviewbar {