JSFiddle - React, Tailwind, and code Playground

HTML

<input id="spinner" type="text" value="0" readonly="readonly">
<div class="actions">
    <div id="up">▲</div>
    <div id="down">▼</div>
</div>

CSS

.actions {
    font-size: 9px;
}
.actions div {
    border: 1px solid #ccc;
    width: 20px;
    text-align: center;
    height: 9px;
    line-height: 7px;
    cursor: pointer;
}

input, .actions {
    float: left;
}

input {
    height: 20px;
    border: 1px solid #ccc;
}

JavaScript

$('up').observe('click', function() { $('spinner').value++; });
$('down').observe('click', function() { $('spinner').value--; });