JSFiddle - React, Tailwind, and code Playground

HTML

<select id="sel" name="terminal_type" onclick="test()"><option value="unknown">Не установлено</option><option id="entr" value="entry" selected >Въездной</option><option value="exit">Выездной</option></select>

<input type="number" name="id_owner" value="1" maxlength="5" min="0" max="65535">

CSS

input { font-size:15px; text-align:center; width:195px;}
select { font-size:15px; width:202px; padding: 1px;}
input::-webkit-inner-spin-button { opacity: 1; }

JavaScript

var n = document.getElementById("sel");
var m= document.getElementById("entr");
var k=n.offsetWidth;
var l=(k/2)-40;
alert(l);
n.style.paddingLeft=l+"px";