Fix UI issues on Implementations on Foreign types

Author: GuillaumeGomez

src/librustdoc/html/static/rustdoc.css

@@ -509,6 +509,9 @@ h4 > code, h3 > code, .invisible > code {
 	top: -9px;
 	left: -13px;
 }
+.methods > .stability {
+	margin-top: -8px;
+}
 
 nav {
 	border-bottom: 1px solid;

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

@@ -407,3 +407,7 @@ kbd {
 .search-results td span.grey {
 	color: #ccc;
 }
+
+.impl-items code {
+	background-color: rgba(0, 0, 0, 0);
+}

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

@@ -401,3 +401,7 @@ kbd {
 .search-results td span.grey {
 	color: #999;
 }
+
+.impl-items code {
+	background-color: rgba(0, 0, 0, 0);
+}