docs: update demo page

docs/lib/dialog-polyfill.css

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+/* Copyright (c) 2013 The Chromium Authors. All rights reserved. */
+._dialog_overlay,dialog+.backdrop{right:0;bottom:0;left:0;position:fixed}dialog{position:absolute;right:0;left:0;display:block;width:-moz-fit-content;width:-webkit-fit-content;width:fit-content;height:-moz-fit-content;height:-webkit-fit-content;height:fit-content;padding:1em;margin:auto;color:#000;background:#fff;border:solid}dialog:not([open]){display:none}dialog+.backdrop{top:0;background:rgba(0,0,0,.1)}._dialog_overlay{top:0}dialog.fixed{position:fixed;top:50%;transform:translate(0,-50%)}

docs/lib/highlight-theme.css

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+/*
+ * Visual Studio 2015 dark style
+ * Author: Nicolas LLOBERA <nllobera@gmail.com>
+ */
+ .hljs{display:block;overflow-x:auto;padding:.5em;background:#1E1E1E;color:#DCDCDC}.hljs-addition,.hljs-deletion{display:inline-block;width:100%}.hljs-keyword,.hljs-link,.hljs-literal,.hljs-name,.hljs-symbol{color:#569CD6}.hljs-link{text-decoration:underline}.hljs-built_in,.hljs-type{color:#4EC9B0}.hljs-class,.hljs-number{color:#B8D7A3}.hljs-meta-string,.hljs-string{color:#D69D85}.hljs-regexp,.hljs-template-tag{color:#9A5334}.hljs-formula,.hljs-function,.hljs-params,.hljs-subst,.hljs-title{color:#DCDCDC}.hljs-comment,.hljs-quote{color:#57A64A;font-style:italic}.hljs-doctag{color:#608B4E}.hljs-meta,.hljs-meta-keyword,.hljs-tag{color:#9B9B9B}.hljs-template-variable,.hljs-variable{color:#BD63C5}.hljs-attr,.hljs-attribute,.hljs-builtin-name{color:#9CDCFE}.hljs-section{color:gold}.hljs-emphasis{font-style:italic}.hljs-strong{font-weight:700}.hljs-bullet,.hljs-selector-attr,.hljs-selector-class,.hljs-selector-id,.hljs-selector-pseudo,.hljs-selector-tag{color:#D7BA7D}.hljs-addition{background-color:#144212}.hljs-deletion{background-color:#600}