style(docs): vertically center theme toggle icon

Author: vnykmshr

docs/_includes/head_custom.html

@@ -7,10 +7,18 @@
   font-size: 1.2rem;
   opacity: 0.7;
   transition: opacity 0.2s;
+  vertical-align: middle;
+  line-height: 1;
+  display: inline-flex;
+  align-items: center;
 }
 .theme-toggle:hover {
   opacity: 1;
 }
+.aux-nav-item {
+  display: flex;
+  align-items: center;
+}
 </style>
 
 <script>