JSFiddle - React, Tailwind, and code Playground

HTML

<div class="page">
<div class="main">Левый блок</div>
<div class="chat">Правый блок</div>
</div>

CSS

.page{
border:1px solid black;
    width:500px;
    min-width:500px;
    height:400px;
    margin:auto;
}

.main {
    margin:10px 0 10px 10px;
    float:left;
    border:1px solid blue;
    width:300px;
    height:380px;
}
    
 .chat{
        margin:10px 10px 0 10px;
float:right;
    border:1px solid blue;
    width:150px;
    height:380px;
}