Fix alignment of magnifying glass in search input

The magnifying glass icon is now centered vertically without relying on
its absolute size. This ensures proper centering, regardless of the
icon's dimensions.

Resolves #3200.

Author: tessarin

root/static/less/search.less

@@ -30,9 +30,10 @@
 .search-group .fa-search {
     color: @input-color;
     font-size: 20px;
-    left: 10px;
+    left: 17px;
     position: absolute;
-    top: 23%;
+    top: 50%;
+    transform: translateY(-50%);
 }
 
 .navbar-nav .search-form {