<!-- Sticky Sidebar Advertisement -->
<div class="sticky-ad-wrapper">
    <div class="sticky-ad-box">
        <button class="sticky-ad-close" onclick="closeStickyAd()">
            ✕
        </button>
        <a href="https://your-ad-link.com" target="_blank">
            <img 
            src="https://your-image-url.com/square-ad.jpg" 
            alt="Advertisement">
        </a>
    </div>
</div>
<style>
/* Sidebar container */
.sticky-ad-wrapper {
    width: 300px;
}
/* Sticky behavior */
.sticky-ad-box {
    position: sticky;
    top: 100px;
    width: 300px;
    height: 300px;
    background: #fff;
    border-radius: 8px;
    overflow: hidden;
    box-shadow: 0 3px 15px rgba(0,0,0,.15);
}
/* Advertisement image */
.sticky-ad-box img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    display: block;
}
/* Close button */
.sticky-ad-close {
    position: absolute;
    top: 6px;
    right: 6px;
    z-index: 10;
    width: 28px;
    height: 28px;
    border-radius: 50%;
    border: none;
    background: rgba(0,0,0,.75);
    color: white;
    font-size: 16px;
    cursor: pointer;
}
/* Mobile layout */
@media (max-width: 900px) {
    .sticky-ad-wrapper {
        width: 100%;
        display: flex;
        justify-content: center;
        margin: 20px 0;
    }
    .sticky-ad-box {
        position: relative;
        top: auto;
        width: min(300px, 100%);
        height: auto;
        aspect-ratio: 1 / 1;
    }
}
</style>
<script>
function closeStickyAd() {
    document.querySelector(".sticky-ad-wrapper").style.display = "none";
}
</script>