<div class="sales"></div>

.sales {
  font-size: 1.5rem;
  color: red;
  text-align: center;
}

const salesMsg = document.querySelector(".sales");

let intervalID = setInterval(() => {
  salesMsg.innerHTML += "<p>Sale ends soon. BUY NOW!</p>";
}, 1000);

setTimeout(() => {
  clearInterval(intervalID);
}, 10000);