[change] : Changed sidebar color to materia-dark

Author: Hayao0819

channels/gnome/airootfs.any/usr/share/calamares/branding/alter/branding.desc

@@ -127,7 +127,7 @@ slideshowAPI: 2
 # branding component also ships a stylesheet.qss. Then they are
 # the corresponding CSS attributes of #sidebarApp.
 style:
-   sidebarBackground:    "#222D32"
+   sidebarBackground:    "#272727"
    sidebarText:          "#FFFFFF"
    sidebarTextSelect:    "#0079ef"
-   sidebarTextHighlight: "#222D32"
+   sidebarTextHighlight: "#272727"