JSFiddle - React, Tailwind, and code Playground

HTML

<body>
<header>
    Text
</header>

<main>
    <nav>
       Navigation
    </nav>
    
    <section id="contentWrapper">
        <section id="contentTitle">
            TITLE
        </section>
    
        <section id="conversationList">
            List
        </section>
    
        <section id="conversation">
            Conversation
        </section>
    </section>
</main>
</body>

CSS

html, body{
    height: 100%; 
    width: 100%;
    margin:0px !important;
}

header{
    position: fixed;
    top: 0;
    height: 60px;
    width: 100%;
    background-color: #777;
    z-index: 1;
}

main{
    float: left;
    padding-top: 60px;
    background-color:black;
    bottom:0px;
    width:100%;
    min-height: calc(100% - 60px);
}

nav{
    float: left;
    width: 15%;
    min-height: 100%;
    background-color: green;
}

#contentTitle{
    float: left;
    width: 98.5%;
    height: 35px;;
    padding-top: 25px;
    padding-left: 1.5%;
    background-color: red;
}

#contentWrapper{
    float: left;
    width: 85%;
    min-height: 100%; 
}

#pageTitle{
    float: left;
    width: 100%;
    height: 40px;
    padding-top: 20px;
    padding-left: 3%;
    background-color: red;
}

#conversationList{
    float: left;
    width: 30%;
    background-color: white;
}

#conversation{
    float: left;
    width: 70%;
    background-color: yellow;
}