JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <div class="main">
        <div class="red">зафлоченный блок</div>
        <div class="content">тут контент</div>
    </div>

</body>

CSS

body{
margin:10px 0;
padding:0;
}
.main{
width:100%;
height:100%;
}

.red{
width:20%;
height:100px;
float:left;
background:red;
border:2px solid #000;
}

.content{
margin-left:22%;
border:1px solid #ccc;
}