Tabbar Layout breaks when DOCTYPE is defined


I’m having trouble understanding the issue with this demo. With the DOCTYPE tag, the page does not render properly. Without the DOCTYPE tag, the page renders as expected. Could you please tell me what I am doing wrong?

                <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
                        html, body {
                        width: 100%;
                        height: 100%;
                        overflow: hidden;
                        margin: 0px;

                <!-- Imports for DHTMLX Tab Bar -->
                <link rel="stylesheet" type="text/css" href="./codebase/dhtmlxtabbar.css">
                <script src="./codebase/dhtmlxcommon.js"></script>
                <script src="./codebase/dhtmlxtabbar.js"></script>

                        function init() {
                                tabbar=new dhtmlXTabBar("a_tabbar", "top");


                                tabbar.addTab("a1", "Tab 1-1", "100px");
                                tabbar.addTab("a2", "Tab 1-2", "100px");
                                tabbar.addTab("a3", "Tab 1-3", "100px");

                                tabbar.setContentHTML("a1", "<br/>This is Tab 1-1");
                                tabbar.setContentHTML("a2", "<br/>This is Tab 1-2");
                                tabbar.setContentHTML("a3", "<br/>This is Tab 1-3");


        <body onload="init()">
                <table style="height:100%;width:100%">
                        <tr style="background:blue;height:40px">
                                        <p> TR 1 height 40px</p>
                                        <div id="a_tabbar" style="height:100%;width:100%"></div>
                        <tr style="background:green;height:40px">
                                        <p>TR 3 height 40px</p>

Demo is attached (80.1 KB)

Fitst of all you can try to use fullscreen 1C layout patternt with header and footer: … ooter.html
Attach to cell A yout tabbar.
And we are offer to use the next doctype:

Hi, maithly
Please, clarify your question.