CSS Animation Filling Bar Example

<!doctype html>
<title>Example</title>
<style>
body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    font-family: sans-serif;
    background-color: #f0f0f0;
}

.progress-container {
    width: 300px;
    height: 20px;
    background-color: #e9ecef;
    border-radius: 10px;
    overflow: hidden;
}

.progress-bar {
    height: 100%;
    background-color: #28a745;
    width: 0%;
    animation: fill-bar 3s cubic-bezier(0.4, 0, 0.2, 1) forwards;
}

@keyframes fill-bar {
    0% { width: 0%; }
    40% { width: 30%; } /* Simulate a pause in loading */
    60% { width: 50%; }
    80% { width: 90%; }
    100% { width: 100%; }
}

@media (prefers-reduced-motion: reduce) {
    .progress-bar {
        /* Optional: Still show progress, but snap in large chunks rather than a smooth slide */
        /* Note: For a real progress bar driven by JS, you'd just use steps() or transition: none */
        animation-timing-function: steps(4, end); 
    }
}
</style>