java web的对齐不会呀

我想把第一张图搞成第二张一样的

img

img


那个运算符和结果哪里搞不来，求神帮帮忙

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      #demo {
        width: 500px;
        margin: 0 auto;
      }
      input {
        margin-left: 30px;
      }
      select {
        margin-left: 10px;
      }
    </style>
  </head>
  <body>
    <div id="demo">
      <p>数1: <input /></p>
      <p>
        运算符:<select>
          <option value="*">*</option>
        </select>
      </p>
      <p>数2: <input /></p>
      <p>结果:<input /></p>
    </div>
  </body>
</html>

img