Minor bug and UI fixes (#6729)

* PLT-6797 - Code block language tag not selectable

* PLT-6771 - Aligning search box with RHS

* PLT-6827 - Fixing link color in error bar

* PLT-6241 - Adding edge detection

webapp/sass/layout/_content.scss

@@ -20,7 +20,6 @@
             // stays on the top and don't get hidden by the
             // search's input block
             float: right;
-            margin-right: -18px;
             padding-right: 0px !important;
             position: relative;
             z-index: 6;