rustdoc: use shorthand background for rustdoc toggle CSS

Author: notriddle

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

@@ -1511,13 +1511,11 @@ details.rustdoc-toggle > summary.hideme > span {
 }
 
 details.rustdoc-toggle > summary::before {
-	background-image: url("toggle-plus-1092eb4930d581b0.svg");
+	background: url("toggle-plus-1092eb4930d581b0.svg") no-repeat top left;
 	content: "";
 	cursor: pointer;
 	width: 16px;
 	height: 16px;
-	background-repeat: no-repeat;
-	background-position: top left;
 	display: inline-block;
 	vertical-align: middle;
 	opacity: .5;
@@ -1598,11 +1596,9 @@ details.rustdoc-toggle[open] > summary.hideme > span {
 
 details.rustdoc-toggle[open] > summary::before,
 details.rustdoc-toggle[open] > summary.hideme::before {
-	background-image: url("toggle-minus-31bbd6e4c77f5c96.svg");
+	background: url("toggle-minus-31bbd6e4c77f5c96.svg") no-repeat top left;
 	width: 16px;
 	height: 16px;
-	background-repeat: no-repeat;
-	background-position: top left;
 	display: inline-block;
 	content: "";
 }