JSFiddle - React, Tailwind, and code Playground
HTML
<input type = "text" class = 'feeld_start' placeholder="Введите число"/>
<input type = "button" class = 'butt' value='+'/>
<div class='output'>1<div/>
CSS
.feeld_start{
background:#FFFED4;
padding:5px 5px;
border:none;
font: normal 20px/26px verdana;
}
.butt{
font: normal 12px/14px verdana;
margin:10px;
}
.butt:hover{
cursor:pointer;
}
.output {
width:100px;
padding:8px;
background:#eee;
margin-top:5px;
}
JavaScript
document.querrySelector('feeld_start')