JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
    <div class="sidebar">
        <ul>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
            <li>1</li>
        </ul>
    </div>
    
    <div class="content">
        <div class="list clearfix">
            <div class="item"></div>
            <div class="item"></div>
            <div class="item"></div>
            <div class="item"></div>
        </div>
        
        <div class="article">
            Какой-то текст
        </div>
    </div>
</div>

CSS

.clearfix{
    height: 1%;
    display: table;
}
.clearfix:after{
content: '. . . . . . . . . . .';
    display: block;
    word-spacing: 99in;
    height: 0;
    overflow: hidden;
    font-size: 0.05em;
    line-height: 0.05em;
}
.main{
    width: 960px;
}
.sidebar{
    float: left;
    width: 200px;
}
.content{
    margin-left: 250px;
    background: #ccc;
}

.list{

    background: red;
}

.item{
    float: left;
    width: 200px;
    height: 50px;
    margin-left: 1%;
    background: #000;
    margin-bottom: 30px;
}
.item:nth-child(3n+1){
    margin-left: 0;
}