JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>
    <body>
        <div class="floor header">
            <a href="http://google.com">Шапка</a>
        </div>
        <div class="floor content">
            <a href="http://google.com">Содержимое</a>
        </div>
        <div class="floor footer">
            <a href="http://google.com">Подвал</a>
        </div>
    </body>
</html>

CSS

.floor{
    border: solid;
    margin-bottom: 5px;
}
.disabled{
    position: relative;
}
.disabled:after{
    display: block;
    position: absolute;
    left: 0;
    top: 0;
    right: 0;
    bottom: 0;
    content: "";
    background-color: rgba(0, 0, 0, 0.5);
    z-index: 1; /* установить в зависимости от контента */
}

JavaScript

var disableContent = false;
setInterval(function()
{
    $(".content").removeClass("disabled");
    
    if (disableContent)
        $(".content").addClass("disabled");
    
    disableContent = !disableContent;
}, 1000);