JSFiddle - React, Tailwind, and code Playground

HTML

<div class="test">
    How it looks:<br />
    <div class="container">
        <button>Lorem</button>
        <button class="small">Dolor</button>
        <button class="small">Sit</button>
    </div>
</div>


<div class="test">
    Seems ok, but the width of upper div should be the same as below:<br />
    <div class="container">
        <button>Lorem</button>
        <button class="small">Dolor</button>

    </div>
</div>

CSS

div.test {
    clear:both;
    width:100%;
}

div.container {
    border:1px solid gray;
    height:50px;
    display: flex;
    flex-direction: column;
    flex-wrap: wrap;
    float:left;
}

button {
    
    height:50px;
    
}

button.small {
    height:20px;
}