Or you can just check in JavaScript after assigning text to h3:

var h3 = document.getElementsByTagName("h3");
h3[0].innerHTML = "Countdown Timer With JS";
//h3[0].innerHTML = "";
if (h3[0].innerHTML == "") {
  h3[0].style.padding = "0px";
} else {
  h3[0].style.padding = "10px";
}