JSFiddle - React, Tailwind, and code Playground

HTML

<div class="fixednav"> <span>some nav stuff</span>
main content which should not be covered by nav</div>

CSS

.fixednav {
    width: 100%;
    height: 30px;
    background: #999;
    line-height:90px;
}
.fixednav > span {
    position:fixed;
    display:block;
    width:100%;
    line-height:30px;
}