JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outer">
    <div class="wrp1">
        <div class="btn">
            <div class="b"></div>
        </div>
        <div class="btn">
            <div class="b"></div>
        </div>
    </div> 
    <div class="wrp2">
        <div class="btn">
            <div class="b"></div>
        </div>
    </div>
</div>

CSS

.outer{
    padding-top: 5px;
    padding-left: 5px;
    border: solid #550000 2px;
    box-sizing: border-box;
    overflow: auto;
}
.wrp1{
    min-width: 66%;
    float: left;
}
.wrp1 .btn{
    width: 50%;
    float: left;
}
.wrp2{
    overflow: hidden;
    min-width: 200px;
}
.btn{
    height: 40px;
    width: 100%;
    padding-right: 5px;
    padding-bottom: 5px;
    box-sizing: border-box;
}
.b{
    background-color: black;
    height: 100%;
    border-radius: 5px;
}