JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
    <div class="content">content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content</div>
    <div class="sidebar">sidebar</div>
</div>

CSS

.main{
    white-space:nowrap;
}
.content{
    display:inline-block;
    white-space:normal;
    vertical-align:top;
    float:right;
    margin-left:100px;
}
.sidebar{
    display:inline-block;
    width:100px;
    vertical-align:top;
}

@media screen and (max-width:400px){
    .content{
        float:none;
        margin-left:0px;
    }
    .sidebar{
        display:block;
        width:auto;
}