Flexbox无法在移动设备上垂直居中

Question

I have made a template using bootstrap and I am using a flexbox to vertically and horizontally center my landing page content. It looks fine on a desktop(chrome and firefox checked), but on mobile(chrome and safari checked) it floats to the top. I have searched the web but have not found a solution that has worked for me.

I have pasted in my code and the live version is at http://webcanvases.com/download-theme/theme/material-theme.html

HTML

<!-- Landing Page -->
<div class="video-bg vertical-center" id="page-top" data-vide-bg="mp4/traffic2">  
    <div class="jumbotron container text-center">
        <h1>Material World<br>Theme</h1> 
        <a data-scroll href="#about"><span class="glyphicon glyphicon-menu-down animated bounce"></span></a>
    </div>
</div>
<!-- Landing Page End -->

CSS

.vertical-center {
    display: flex;
    justify-content: center;
    align-items: center;
}

.video-bg {
    height: 800px;
    min-width: 100%;
}

Answer 1

It's not working because you have to set the flex properties on an outer container. Then the elements on the inside will follow the flex properties.

 .vertical-center { display: flex; align-items: center; justify-content: center; height: 100vh; background: #ccc; } .video-bg { width: 400px; height: 300px; background: yellow; } 

 <div class="vertical-center"> <div class="video-bg"></div> </div>