Match style of navbar icons in current docs

Author: speth

source/_static/css/custom.css

@@ -36,6 +36,10 @@ p + div.math {
     text-align: center;
  }
 
+.theme-switch-button span {
+    padding: 1.6em;
+}
+
 /* Make "tip" background color different from "versionadded" */
 .admonition.tip,
 div.admonition.tip {

source/conf.py

@@ -116,13 +116,6 @@
     },
     "github_url": "https://github.com/Cantera/cantera",
     "header_links_before_dropdown": 6,
-    "icon_links": [
-        {
-            "name": "PyPI",
-            "url": "https://pypi.org/project/cantera",
-            "icon": "fa-solid fa-box",
-        },
-    ],
     # "logo": {
     #     "text": "PyData Theme",
     #     "image_dark": "_static/logo-dark.svg",