fix: Avoid scrolling to top when opening search (#440)

Before, the the content always scrolled to the top when opening the
search on content pages.

Co-authored-by: Robert Schuster <77234379+therobrob@users.noreply.github.com>

Author: MoritzWeber0

assets/sass/search.scss

@@ -147,7 +147,7 @@ $search-z-index: 12;
 
 .o-search {
   &--contentpage {
-    position: absolute;
+    position: fixed;
     display: none;
     opacity: 0;
     visibility: hidden;

layouts/_default/baseof.html

@@ -19,7 +19,7 @@
         {{ if not .IsHome }}
           <div
             id="search"
-            class="o-search o-search--contentpage"
+            class="o-search o-container o-search--contentpage"
             data-placeholder="{{ T "search.placeholder" }}"
             data-label="{{ T "search.label" }}"
           ></div>