Auto merge of #55126 - GuillaumeGomez:improve-search-tabs, r=QuietMisdreavus

improve search tabs look

Fixes #55056.

![screenshot from 2018-10-16 19-06-48](https://user-images.githubusercontent.com/3050060/47034247-1e08b280-d177-11e8-9c1e-c7320af9b561.png)

![screenshot from 2018-10-16 19-09-39](https://user-images.githubusercontent.com/3050060/47034255-2365fd00-d177-11e8-8686-4765d3e56ff5.png)

With this, I think it'll be more obvious.

cc @memoryruins

r? @QuietMisdreavus

src/librustdoc/html/static/rustdoc.css

@@ -1086,17 +1086,14 @@ pre.rust {
 	float: left;
 	width: 33.3%;
 	text-align: center;
-	border-bottom: 1px solid;
 	font-size: 18px;
 	cursor: pointer;
+	border-top: 2px solid;
 }
 
-#titles > div.selected {
-	border-bottom: 3px solid;
-}
-
-#titles > div:hover {
-	border-bottom: 3px solid;
+#titles > div:not(:last-child):not(.selected) {
+	margin-right: 1px;
+	width: calc(33.3% - 1px);
 }
 
 #titles > div > div.count {

src/librustdoc/html/static/themes/dark.css

@@ -300,16 +300,13 @@ pre.ignore:hover, .information:hover + pre.ignore {
 	border-color: black;
 }
 
-#titles > div {
-	border-bottom-color:  #ccc;
+#titles > div:not(.selected) {
+	background-color: #252525;
+	border-top-color: #252525;
 }
 
-#titles > div.selected {
-	border-bottom-color: #0078ee;
-}
-
-#titles > div:hover {
-	border-bottom-color: #0089ff;
+#titles > div:hover, #titles > div.selected {
+	border-top-color: #0089ff;
 }
 
 #titles > div > div.count {

src/librustdoc/html/static/themes/light.css

@@ -294,16 +294,13 @@ pre.ignore:hover, .information:hover + pre.ignore {
 	border-color: black;
 }
 
-#titles > div {
-	border-bottom-color:  #ccc;
+#titles > div:not(.selected) {
+	background-color: #e6e6e6;
+	border-top-color: #e6e6e6;
 }
 
-#titles > div.selected {
-	border-bottom-color: #0078ee;
-}
-
-#titles > div:hover {
-	border-bottom-color: #0089ff;
+#titles > div:hover, #titles > div.selected {
+	border-top-color: #0089ff;
 }
 
 #titles > div > div.count {