Unify sidebar buttons to use the same image

Author: GuillaumeGomez

src/librustdoc/html/static/css/rustdoc.css

@@ -55,6 +55,9 @@ xmlns="http://www.w3.org/2000/svg" fill="black" height="18px">\
 	--collapse-arrow-image: url('data:image/svg+xml,<svg width="16" height="16" viewBox="0 0 16 16" \
 	enable-background="new 0 0 16 16" xmlns="http://www.w3.org/2000/svg"><path fill="none" \
 	d="M3,8l4,4l4,-4m-4,4M3,4l4,4l4,-4" stroke="black" stroke-width="2"/></svg>');
+	--hamburger-image: url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" \
+		viewBox="0 0 22 22" fill="none" stroke="black">\
+		<path d="M3,5h16M3,11h16M3,17h16" stroke-width="2.75"/></svg>');
 }
 
 :root.sans-serif {
@@ -2402,9 +2405,7 @@ However, it's not needed with smaller screen width because the doc/code block is
 	use hamburger button */
 .src #sidebar-button > a:before, .sidebar-menu-toggle:before {
 	/* hamburger button image */
-	content: url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" \
-		viewBox="0 0 22 22" fill="none" stroke="black">\
-		<path d="M3,5h16M3,11h16M3,17h16" stroke-width="2.75"/></svg>');
+	content: var(--hamburger-image);
 	opacity: 0.75;
 }
 .sidebar-menu-toggle:hover:before,
@@ -2413,17 +2414,6 @@ However, it's not needed with smaller screen width because the doc/code block is
 	opacity: 1;
 }
 
-/* src sidebar button opens a folder view */
-.src #sidebar-button > a:before {
-	/* folder image */
-	content: url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" \
-		viewBox="0 0 22 22" fill="none" stroke="black">\
-		<path d="M16,9v-4h-6v-1l-2,-2h-4l-2,2v16h13L21,9h-15L2,19" stroke-width="1.25"/>\
-		<path d="M15,7h-11v3" stroke-width="0.75"/>\
-		<path d="M3.75,10v1.25" stroke-width="0.375"/></svg>');
-	opacity: 0.75;
-}
-
 /* Media Queries */
 
 /* Make sure all the buttons line wrap at the same time */