<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport"
content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0,minimum-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<script src="node_modules/bootstrap/dist/js/bootstrap.min.js"></script>
<link href="node_modules/bootstrap/dist/css/bootstrap.min.css" rel="stylesheet"/>
<link href="node_modules/@fortawesome/fontawesome-free/css/all.min.css" rel="stylesheet"/>
<title>Back Site</title>
</head>
<body>
<form id="frm-items" class="row g-3">
<div class="d-flex flex-column w-25 my-5 mx-3">
Выберите тип данных
<div>
<select id="type" class="form-select" >
<option value="int">Число</option>
<option value="string">Строка</option>
</select>
</div>
Введите первое значение
<input id="first" class="form-control"></input>
Введите второе значение
<input id="second" class="form-control"></input>
Выберите операцию
<div>
<button type="button" class="btn btn-primary" id="buttonSum">Sum</button>
<button type="button" class="btn btn-primary" id="buttonMinus">Minus</button>
<button type="button" class="btn btn-primary" id="buttonReverse">Reverse</button>
<button type="button" class="btn btn-primary" id="buttonComparison">Comparison</button>
</div>
Результат
<input id="res" class="form-control"></input>
</div>
</form>
<script src="script.js"></script>
</body>
</html>