JSFiddle - React, Tailwind, and code Playground

HTML

<h1 class="main rotate">TEXT</h1>









<!-- Notes and Centered red box -->
<div class="centeredbox"></div>
<div class="note">"<span class="green">TEXT</span>" should always be in the middle of the page. The absolute center is represented by <span class="red">red box</span>. How might I do this CSS / HTML only?</div>

CSS

html {
    padding:0;
    margin:0;
    font-size:100%;
}
h1 {
    text-transform: uppercase;
    white-space: nowrap;
    text-align: center;
    position: fixed;
    margin: 50vh;
    opacity: 1;
    -webkit-transition: opacity 300ms ease;
    -moz-transition: opacity 300ms ease;
    transition: opacity 300ms ease;
    -webkit-transform: translateZ(0);
    -moz-transform: translateZ(0);
    -ms-transform: translateZ(0);
    -o-transform: translateZ(0);
    transform: translateZ(0);
}
.rotate {
    -webkit-transform-origin: 0 50%;
    -moz-transform-origin: 0 50%;
    -ms-transform-origin: 0 50%;
    -o-transform-origin: 0 50%;
    transform-origin: 0 50%;
    -webkit-transform: rotate(-90deg) translate(-50%, 50%);
    -moz-transform: rotate(-90deg) translate(-50%, 50%);
    -ms-transform: rotate(-90deg) translate(-50%, 50%);
    -o-transform: rotate(-90deg) translate(-50%, 50%);
    transform: rotate(-90deg) translate(-50%, 50%);
}
.main {
    color:green;
    font-size: 60px;
    font-family:'helvetica neue';
    font-weight: normal;
    font-style: normal;
}




/* notes */
.note {
    font-size:12px;
    line-height:1.5;
    left:25px;
    bottom:25px;
    position:fixed;
}
.centeredbox{
     position:absolute;
     width:10px;
     height:10px;
     z-index:15;
     margin: 50vh;
     background:red;
}
span.red {
    color:red;
}
span.green {
    color:green;
}