rustdoc: clean up CSS #titles using flexbox

This commit allows it to stop manually specifying pixel heights for the tabs
on search result pages. There's less messing with manual breakpoints and
less complex CSS selectors.

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

@@ -1378,27 +1378,19 @@ pre.rust {
 }
 
 #titles {
-	height: 35px;
+	display: flex;
+	flex-direction: row;
+	gap: 1px;
+	margin-bottom: 4px;
 }
 
 #titles > button {
-	float: left;
-	width: 33.3%;
 	text-align: center;
 	font-size: 1.125rem;
 	cursor: pointer;
 	border: 0;
 	border-top: 2px solid;
-}
-
-#titles > button:first-child:last-child {
-	margin-right: 1px;
-	width: calc(100% - 1px);
-}
-
-#titles > button:not(:last-child) {
-	margin-right: 1px;
-	width: calc(33.3% - 1px);
+	flex: 1;
 }
 
 #titles > button > div.count {
@@ -1895,12 +1887,7 @@ in storage.js plus the media query with (min-width: 701px)
 	}
 
 	#titles > button > div.count {
-		float: left;
-		width: 100%;
-	}
-
-	#titles {
-		height: 50px;
+		display: block;
 	}
 
 	/* Because of ios, we need to actually have a full height sidebar title so the
@@ -2031,10 +2018,6 @@ in storage.js plus the media query with (min-width: 701px)
 }
 
 @media (max-width: 464px) {
-	#titles, #titles > button {
-		height: 73px;
-	}
-
 	#crate-search {
 		border-radius: 4px;
 	}