html input year
<form>
<style>
div {
margin-bottom: 10px;
}
input:invalid+span:after {
content: '✖';
padding-left: 5px;
}
input:valid+span:after {
content: '✓';
padding-left: 5px;
}
</style>
<div>
<label for="balloons">Number of balloons to order (multiples of year):</label>
<input id="balloons" type="number" name="balloons" value = "2021" step="1" min="2000" max="2050" required >
<span class="validity"></span>
</div>
<div>
<input type="submit">
</div>
</form>