Apply suggestion from @StanFromIreland

Co-authored-by: Stan Ulbrych <stan@python.org>

Author: sepehr-rs

python_docs_theme/static/pydoctheme.css

@@ -750,7 +750,7 @@ div.genindex-jumpbox a {
         top: 0;
         inset-inline-start: 0;
         transition: transform 400ms ease;
-        transform: translateX(-100%);
+        transform: translateX(calc(-100% - 10px));
         width: 300px;
         height: 100%;
         background-color: #eee;