diff --git a/doc/_static/css/custom.css b/doc/_static/css/custom.css
index 2fd1045d81e..2d365419c38 100644
--- a/doc/_static/css/custom.css
+++ b/doc/_static/css/custom.css
@@ -738,21 +738,21 @@ kbd, .kbd,
     border: none;
 }
 
-.wy-side-nav-search, .wy-menu-vertical a, .wy-menu-vertical a span.toctree-expand,
-.wy-menu-vertical li.toctree-l2 a span.toctree-expand {
+.wy-menu-vertical a button.toctree-expand,
+.wy-menu-vertical li.toctree-l2 a button.toctree-expand {
     color: var(--navbar-level-3-color);
     opacity: 0.9;
-    margin-right: 8px;
+    margin-right: 6px;
 }
 
-.wy-side-nav-search, .wy-menu-vertical a, .wy-menu-vertical a:hover span.toctree-expand,
-.wy-menu-vertical li.toctree-l2 a:hover span.toctree-expand {
+.wy-menu-vertical a:hover button.toctree-expand,
+.wy-menu-vertical li.toctree-l2 a:hover button.toctree-expand {
     color: var(--navbar-level-2-color);
     opacity: 1;
 }
 
-.wy-side-nav-search, .wy-menu-vertical a, .wy-menu-vertical a:active span.toctree-expand,
-.wy-menu-vertical li.toctree-l2 a:active span.toctree-expand {
+.wy-menu-vertical a:active button.toctree-expand,
+.wy-menu-vertical li.toctree-l2 a:active button.toctree-expand {
     color: var(--navbar-level-1-color);
     opacity: 1;
 }