JSFiddle - React, Tailwind, and code Playground

HTML

<div id="foo"></div>
<div id="bar"></div>
<div id="baz"></div>

CSS

#foo { 
    background: red;
    height: 100px;
    position: relative;
        z-index: 3;
    width: 100px;
}

#foo:hover + #bar {  display: block; }
#foo:hover + #bar + #baz {  height: 100%; }

#bar {
    background: blue;
    display: none;
    height: 100px;
    position: relative;
        z-index: 2;
    width: 100px;
}
#baz {
    background: green;
    height: 0;
    position: fixed;
        top: 0;
        left: 0;
        z-index: 1;
    width: 100%;
}