JSFiddle - React, Tailwind, and code Playground

HTML

<div class="select"><select><option>Mon</option><option>option</option></select><div>

CSS

.select {
    display : inline-block;
    border-radius : 7px 0 0 7px;
    border : 2px #ddd solid;
    padding-left : 2px;
}

select {
    margin : 0;
    border : none;
}