z-index如何全屏工作？

Question

目前我遇到Twitch的iframe流视频问题。当我选择全屏时，z-index不再有效。它隐藏在iframe下。请指导大家如何解决。谢谢阅读。    https://codepen.io/pobby/pen/bKbNZo

<div id="twitch-embed">
        <div class="cr_display_logo">TEST</div></div>

<!-- Load the Twitch embed script -->
<script src="https://embed.twitch.tv/embed/v1.js"></script>
<script type="text/javascript">
var embed = new Twitch.Embed("twitch-embed", {
width: 854,
height: 480,
channel: "tonyteo2018",
layout: "video",
autoplay: false
});

embed.addEventListener(Twitch.Embed.VIDEO_READY, () => {
var player = embed.getPlayer();
player.play();
});
</script>