improve ToC height responsiveness

assets/css/common/post-single.css

@@ -279,6 +279,8 @@
         top: 100px;
         width: 300px;
         font-size: .9em;
+        max-height: calc(100% - 150px);
+        overflow: auto;
     }
 }
 

assets/css/includes/scroll-bar.css

@@ -60,4 +60,15 @@
         width: 19px;
         height: 11px;
     }
+}
+
+/* side ToC */
+
+.toc.side::-webkit-scrollbar-thumb {
+    border: none;
+    background: var(--secondary);
+}
+
+.toc.side::-webkit-scrollbar {
+    width: 8px;
 }