<div class="container-balance">
    <h3></h3>
</div>
<div class="container-spin">
    <button><img src="img/spin (2).jpg" alt="spin" height="98px" 
    width="100px"></button>
</div>

let cash = 10000;

const h3 = document.querySelector('h3');
const button = document.querySelector('button');

function updateHeader() {
  h3.innerText = `Ваш баланс: ${cash} руб.`;
}

updateHeader();

function Random(max) {
  return Math.ceil(Math.random() * max);
}

function spin() {
  const max = Random(9);
  if ([1, 2, 3].includes(max)) {
    cash = cash + 200;
    updateHeader();
  }
}

button.addEventListener('click', spin);