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')