Flip chevrons when subtree is expanded (#1584)

Author: gabalafou

src/pydata_sphinx_theme/assets/styles/components/_navbar-links.scss

@@ -40,15 +40,15 @@
     ~ ul {
       display: none;
     }
-    ~ label i {
+    ~ label .fa-chevron-down {
       transform: rotate(0deg);
     }
   }
   .toctree-checkbox:checked {
     ~ ul {
       display: block;
     }
-    ~ label i {
+    ~ label .fa-chevron-down {
       transform: rotate(180deg);
     }
   }