add nav list left margin to docs css [skip ci]

Author: OwenMcDonnell

sdk/python/packages/flet/docs/extras/css/mkdocstrings.css

@@ -86,3 +86,11 @@ code.doc-symbol-command::after {
 }
 
 /* Command symbol */
+
+
+
+/* Proposals */
+
+.md-nav__item--section > .md-nav > .md-nav__list {
+  margin-left: 0.4rem;
+}