Adjust GNOME-Shell so that it uses a Guix theme by default.

Patch by Ludovic Courtès <ludo@gnu.org>.

diff -ur a/data/gnome-shell-theme.gresource.xml b/data/gnome-shell-theme.gresource.xml
--- a/data/gnome-shell-theme.gresource.xml	2019-12-11 15:06:31.000000000 -0500
+++ b/data/gnome-shell-theme.gresource.xml	2019-12-21 00:31:55.895866241 -0500
@@ -19,6 +19,8 @@
     <file>no-events.svg</file>
     <file>no-notifications.svg</file>
     <file>noise-texture.png</file>
+    <file>guix-background.png</file>
+    <file>guix-logo.png</file>
     <file>pad-osd.css</file>
     <file alias="icons/pointer-double-click-symbolic.svg">pointer-double-click-symbolic.svg</file>
     <file alias="icons/pointer-drag-symbolic.svg">pointer-drag-symbolic.svg</file>
diff -ur a/data/theme/gnome-shell-sass/_common.scss b/data/theme/gnome-shell-sass/_common.scss
--- a/data/theme/gnome-shell-sass/_common.scss	2019-12-11 15:06:31.000000000 -0500
+++ b/data/theme/gnome-shell-sass/_common.scss	2019-12-21 00:33:49.495832135 -0500
@@ -1994,7 +1994,16 @@
   }
 }
 
-  .login-dialog-logo-bin { padding: 24px 0px; }
+  .login-dialog-logo-bin {
+      /* Make it a bit narrower than .login-dialog-user-list.  */
+      width: 12em;
+      height: 8em;
+      background: url(resource:///org/gnome/shell/theme/guix-logo.png);
+      background-color: transparent;
+      background-repeat: no-repeat;
+      background-size: contain;
+      background-position: center; }
+
   .login-dialog-banner { color: darken($osd_fg_color,10%); }
   .login-dialog-button-box { spacing: 5px; }
   .login-dialog-message-warning { color: $warning_color; }
@@ -2143,9 +2152,10 @@
 }
 
 #lockDialogGroup {
-  background: lighten(#2e3436, 8%) url(resource:///org/gnome/shell/theme/noise-texture.png);
-  background-repeat: repeat;
-}
+  background: lighten(#2e3436, 8%) url(resource:///org/gnome/shell/theme/guix-background.png);
+  background-repeat: no-repeat;
+  background-size: cover;
+  background-position: center; }
 
 #screenShieldNotifications {
   StButton#vhandle, StButton#hhandle {
380d4e7c514f9f1cdaec60b3013e9c08'>etc</a>/<a href='/guix/log/etc/teams?id=d3e2b68e380d4e7c514f9f1cdaec60b3013e9c08'>teams</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/etc/teams?id=d3e2b68e380d4e7c514f9f1cdaec60b3013e9c08&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2024-03-19 03:40:08 -0400'>2024-03-19</span></td><td><a href='/guix/commit/etc/teams?id=a8ba2f3507d03ec77506a03bf84d62f9cb439f8e'>teams: qt: Remove erroneous comment at top of scripts.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/teams/qt/common.scm: Remove erroneous comment.
* etc/teams/qt/qt-manifest.scm: Likewise.
* etc/teams/qt/qt5-manifest.scm: Likewise.

Change-Id: I87a0ea669caa0ba5049b48a4f04fda58518c3f05
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2024-01-04 12:31:45 +0200'>2024-01-04</span></td><td><a href='/guix/commit/etc/teams?id=8b559b37eafbf51fe4a602c091754a38b8ad28f7'>etc: Add rust-team manifest.</a><span class='msg-avail'>...<span class='msg-tooltip'>Change-Id: Ie43bd4a88d35270dcac7baaabeafbcc3a755db1e
</span></span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2023-08-22 12:32:20 -0400'>2023-08-22</span></td><td><a href='/guix/commit/etc/teams?id=0b994bb9b10b381376f1dfd8bd2bc9173ede2a66'>etc: Add Qt manifests for Qt maintenance.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/teams/qt/common.scm: New file.
* etc/teams/qt/qt-manifest.scm: Likewise.
* etc/teams/qt/qt5-manifest.scm: Likewise.
</span></span></td><td>Maxim Cournoyer</td></tr>