[Doc] Simplify addition of "Community" link

doc/sphinx/_static/custom.css

@@ -1,3 +1,7 @@
+html {
+    --pst-icon-external-link: "";
+}
+
 p + div.math {
     /* Remove post-paragraph space ahead of equation to center vertically */
     margin-top: -1.15em;
@@ -8,8 +12,3 @@ p + div.math {
     display: none;
     visibility: hidden;
 }
-
-.bd-header .navbar-header-items__center {
-    /* Reduce gap between Sphinx sections and ones added via cantera-org-links.html */
-    column-gap: normal;
-}

doc/sphinx/_templates/cantera-org-links.html

@@ -1,7 +0,0 @@
-<ul class="bd-navbar-elements navbar-nav">
-    <li class="nav-item">
-        <a class="nav-link nav-internal" href="/community.html">
-            Community
-        </a>
-    </li>
-</ul>

doc/sphinx/conf.py

@@ -311,7 +311,11 @@ html_theme = 'pydata_sphinx_theme'
 
 html_theme_options = {
     "show_toc_level": 2,
-    "navbar_center": ["navbar-nav", "cantera-org-links"],
+    "navbar_center": ["navbar-nav"],
+    "external_links": [
+      {"name": "Community", "url": "/community.html"},
+    ],
+    "header_links_before_dropdown": 6,
     "navbar_align": "left",
     "navbar_end": ["version-switcher", "theme-switcher", "navbar-icon-links"],
     "show_prev_next": False,