Gnome-Shell-3.24&3.26: [PanelCorner] Fix incorrect transitions

* Clean up unneeded values.
* Set correct properties for proper transitions.

Otherwise these logs are recorded:
"setup_framebuffers: assertion 'width > 0' failed"

This commit fixes the issue: #475.

shell/sass/gnome-shell/3.24/_common.scss

@@ -1085,23 +1085,20 @@ StScrollBar {
     spacing: 0;
   }
 
-  .panel-corner {
+  .panel-corner { // unset all properties
     -panel-corner-radius: 0;
-    -panel-corner-background-color: $panel_bg_color;
-    -panel-corner-border-width: 2px;
+    -panel-corner-background-color: $panel_hidden_fill_color;
+    -panel-corner-border-width: 0;
     -panel-corner-border-color: transparent;
+    transition-duration: 0s;
 
-    transition-timing-function: $slope_slow;
-    transition-duration: $duration_long;
-
-    &:hover {
+    &:hover,
+    &:focus {
       background-color: $panel_hidden_fill_color;
       box-shadow: inset 0 2px $osd_fill_color;
     }
     &:active,
-    &:overview,
-    &:focus {
-      -panel-corner-border-color: transparent;
+    &:overview {
       background-color: $panel_hidden_fill_color;
       box-shadow: inset 0 2px $osd_indicator_color;
     }
@@ -1111,6 +1108,7 @@ StScrollBar {
     &.unlock-screen {
       -panel-corner-radius: 0;
       -panel-corner-background-color: transparent;
+      -panel-corner-border-width: 0;
       -panel-corner-border-color: transparent;
     }
 

shell/sass/gnome-shell/3.26/_common.scss

@@ -1122,23 +1122,20 @@ StScrollBar {
     spacing: 0;
   }
 
-  .panel-corner {
+  .panel-corner { // unset all properties
     -panel-corner-radius: 0;
     -panel-corner-background-color: $panel_hidden_fill_color;
-    -panel-corner-border-width: 2px;
+    -panel-corner-border-width: 0;
     -panel-corner-border-color: transparent;
+    transition-duration: 0s;
 
-    transition-timing-function: $slope_slow;
-    transition-duration: $duration_long;
-
-    &:hover {
+    &:hover,
+    &:focus {
       background-color: $panel_hidden_fill_color;
       box-shadow: inset 0 2px $osd_fill_color;
     }
     &:active,
-    &:overview,
-    &:focus {
-      -panel-corner-border-color: transparent;
+    &:overview {
       background-color: $panel_hidden_fill_color;
       box-shadow: inset 0 2px $osd_indicator_color;
     }
@@ -1148,6 +1145,7 @@ StScrollBar {
     &.unlock-screen {
       -panel-corner-radius: 0;
       -panel-corner-background-color: transparent;
+      -panel-corner-border-width: 0;
       -panel-corner-border-color: transparent;
     }
 

shell/sass/parse-sass.sh

@@ -25,7 +25,7 @@ GNOME_MINOR_VERSION="`echo $GNOME_VERSION | cut -d'.' -f2`"
 if [ -e $GNOME_SHELL ] && [ $GNOME_MAJOR_VERSION -eq "3" ] && \
     [ $GNOME_MINOR_VERSION -ge "18" ]; then
 
-    if [ $GNOME_MINOR_VERSION -gt "24" ]; then
+    if [ $GNOME_MINOR_VERSION -gt "23" ]; then
         GNOME_SCSS_VERSION=$GNOME_MAJOR_VERSION.26
     else
         GNOME_SCSS_VERSION=$GNOME_MAJOR_VERSION.24