Rollup merge of rust-lang#105155 - notriddle:notriddle/flexbox-help-settings-buttons, r=GuillaumeGomez

rustdoc: clean up help and settings button CSS

The old version of this code specified a bunch of different numbers that had to line up just right to get the size it wanted. This version uses flexbox centering, specifies the font size, and lets the browser figure out the rest of the layout automatically.

Preview: http://notriddle.com/notriddle-rustdoc-demos/flexbox-help-settings-buttons/test_dingus/

Author: matthiaskrgr

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

@@ -908,6 +908,7 @@ so that we can apply CSS-filters to change the arrow color in themes */
 
 .popover {
 	position: absolute;
+	top: 100%;
 	right: 0;
 	z-index: 2;
 	display: block;
@@ -1357,22 +1358,24 @@ a.test-arrow:hover {
 }
 #settings-menu, #help-button {
 	margin-left: 4px;
-	outline: none;
+	display: flex;
 }
 
 #settings-menu > a, #help-button > a, #copy-path {
 	width: 33px;
-	line-height: 1.5;
 }
 
 #settings-menu > a, #help-button > a {
-	padding: 5px;
-	height: 100%;
-	display: block;
+	display: flex;
+	align-items: center;
+	justify-content: center;
 	background-color: var(--button-background-color);
 	border: 1px solid var(--border-color);
 	border-radius: 2px;
 	color: var(--settings-button-color);
+	/* Rare exception to specifying font sizes in rem. Since this is acting
+	   as an icon, it's okay to specify their sizes in pixels. */
+	font-size: 20px;
 }
 
 #settings-menu > a:hover, #settings-menu > a:focus,
@@ -1408,14 +1411,6 @@ a.test-arrow:hover {
 	animation: rotating 2s linear infinite;
 }
 
-#help-button > a {
-	text-align: center;
-	/* Rare exception to specifying font sizes in rem. Since this is acting
-	   as an icon, it's okay to specify their sizes in pixels. */
-	font-size: 20px;
-	padding-top: 2px;
-}
-
 kbd {
 	display: inline-block;
 	padding: 3px 5px;
@@ -1658,10 +1653,6 @@ in storage.js
 		content: "Since ";
 	}
 
-	#copy-path {
-		display: none;
-	}
-
 	/* Hide the logo and item name from the sidebar. Those are displayed
 	   in the mobile-topbar instead. */
 	.sidebar .sidebar-logo,
@@ -1795,8 +1786,8 @@ in storage.js
 		border-bottom: 1px solid;
 	}
 
-	/* We don't display the help button on mobile devices. */
-	#help-button {
+	/* We don't display these buttons on mobile devices. */
+	#copy-path, #help-button {
 		display: none;
 	}