JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>
    
    <head lang="en">
        <meta charset="UTF-8">
        <title></title>
    </head>
    
    <body>
        <form>
            <input type='text' id='main_input'>
            <input type='submit' onclick='EnterCommand(); return false;' value='Ввести команду'>
        </form>
        <div id='main_output'></div>
        <script src='Main.js'></script>
    </body>

</html>

CSS

input[type='text'] {
    background: #000;
}

JavaScript

var main_input = document.getElementById('main_input');
var main_output = document.getElementById('main_output');

var money = 0;

function EnterCommand() {
    if (main_input.value == 'csx_guard') {
        SendMessage();
        return;
    }

    main_output.innerHTML = 'Такой команды не существует';
}

function SendMessage() {
    main_output.innerHTML = 'test';
}