Make headings anchor hidden by default and show on hover

Author: GuillaumeGomez

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

@@ -765,14 +765,30 @@ nav.sub {
 h2.section-header > .anchor {
 	padding-right: 6px;
 }
-.doc-anchor {
-	margin-right: 6px;
+a.doc-anchor {
+	color: var(--main-color);
+	display: none;
+	position: absolute;
+	left: -17px;
+	/* We add this padding so that when the cursor moves from the heading's text to the anchor,
+	   the anchor doesn't disappear. */
+	padding-right: 5px;
+	/* And this padding is used to make the anchor larger and easier to click on. */
+	padding-left: 3px;
+}
+*:hover > .doc-anchor {
+	display: block;
+}
+/* If the first element of the top doc block is a heading, we don't want to ever display its anchor
+because of the `[-]` element which would overlap with it. */
+.top-doc > .docblock > *:first-child > .doc-anchor {
+	display: none !important;
 }
 
 .main-heading a:hover,
 .example-wrap .rust a:hover,
 .all-items a:hover,
-.docblock a:not(.test-arrow):not(.scrape-help):not(.tooltip):hover,
+.docblock a:not(.test-arrow):not(.scrape-help):not(.tooltip):hover:not(.doc-anchor),
 .docblock-short a:not(.test-arrow):not(.scrape-help):not(.tooltip):hover,
 .item-info a {
 	text-decoration: underline;