Use a magnifying glass instead of a text "Go" for the search button

additionally:
- Change placeholder text from "Search" to "Search...", which seems more common
- CSS changes: Use a fixed height to make sure search field and button have the
  same hight. Also reduce button width a little because the icon needs less
  space.

sphinx/themes/basic/searchbox.html

@@ -13,7 +13,7 @@ <h3 id="searchlabel">{{ _('Quick search') }}</h3>
     <div class="searchformwrapper">
     <form class="search" action="{{ pathto('search') }}" method="get">
       <input type="text" name="q" aria-labelledby="searchlabel" autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false"/>
-      <input type="submit" value="{{ _('Go') }}" />
+      <input type="submit" value="{{ _('🔍') }}" />
     </form>
     </div>
 </search>

sphinx/themes/basic/searchfield.html

@@ -14,8 +14,8 @@
 <search id="searchbox" style="display: none" role="search">
     <div class="searchformwrapper">
     <form class="search" action="{{ pathto('search') }}" method="get">
-      <input type="text" name="q" aria-labelledby="searchlabel" autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false" placeholder="Search"/>
-      <input type="submit" value="{{ _('Go') }}" />
+      <input type="text" name="q" aria-labelledby="searchlabel" autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false" placeholder="Search..."/>
+      <input type="submit" value="{{ _('🔍︎') }}" />
     </form>
     </div>
 </search>

sphinx/themes/basic/static/basic.css.jinja

@@ -93,16 +93,17 @@ div.sphinxsidebar #searchbox form.search {
 
 div.sphinxsidebar #searchbox input[type="text"] {
     float: left;
-    width: 80%;
-    padding: 0.25em;
+    width: 84%;
+    height: 2em;
+    padding-left: 0.4em;
     box-sizing: border-box;
 }
 
 div.sphinxsidebar #searchbox input[type="submit"] {
     float: left;
-    width: 20%;
+    width: 16%;
+    height: 2em;
     border-left: none;
-    padding: 0.25em;
     box-sizing: border-box;
 }