JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="content">
        <h1>HEADER1 HEADER1 HEADER1 HEADER1 HEADER1 HEADER1 HEADER1<h1>
    </div>
    <div id="menu">xcvcxcxvcvxcvzxczxczgd</div>
</div>

CSS

body{
    display: flex;
}

#container{
    display: flex;
    flex-basis: 300px;
    overflow: hidden;
}

#content{
    display: block;
    height: 300px;
    background-color: red;
    flex-grow: 1;
    flex-shrink: 1;
}

h1, h2{
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}


#menu{
    display: flex;
    flex-grow: 0;
    height: 300px;
    background-color: blue;
    flex-shrink: 0;
}