docs: Update CSS with mkdocstrings recommended style

docs/custom.css

@@ -1,14 +1,38 @@
+/* Indentation. */
 div.doc-contents:not(.first) {
   padding-left: 25px;
   border-left: 4px solid rgba(230, 230, 230);
   margin-bottom: 80px;
 }
 
-h4.doc::before {
+/* Don't capitalize names. */
+h5.doc-heading {
+  text-transform: none !important;
+}
+
+/* Don't use vertical space on hidden ToC entries. */
+h6.hidden-toc {
+  margin: 0 !important;
+  position: relative;
+  top: -70px;
+}
+h6.hidden-toc::before {
   margin-top: 0 !important;
   padding-top: 0 !important;
 }
 
-h5.doc-heading {
-  text-transform: none !important;
+/* Don't show permalink of hidden ToC entries. */
+h6.hidden-toc a.headerlink {
+  display: none;
+}
+
+/* Avoid breaking parameters name, etc. in table cells. */
+td code {
+  word-break: normal !important;
+}
+
+/* For pieces of Markdown rendered in table cells. */
+td p {
+  margin-top: 0 !important;
+  margin-bottom: 0 !important;
 }

docs/reference/api.md

@@ -1,2 +1 @@
 ::: aria2p.api
-