ureech,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.container {
width: 500px;
height: 15px;
background-color: #008000;
transition: width 2.6s ease;
}
</style>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
<script>
$(function() {
let container = $('.container');
const addPanel = function() {
container.width(container.width() - 250)
}
window.setTimeout(() => addPanel(), 300)
});
</script>
</head>
<body>
<div class="container"></div>
</body>
</html>