css大图片居中

img {
  display: block;
  margin-left: auto;
  margin-right: auto;
}

.container {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh; /* 使容器高度占满整个视口 */
}

img {
  max-width: 100%;
  max-height: 100%;
}

.container {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh; /* 使容器高度占满整个视口 */
}

img {
  max-width: 100%;
  max-height: 100%;
}

<picture>
  <source srcset="large.jpg" media="(min-width: 1200px)">
  <source srcset="medium.jpg" media="(min-width: 768px)">
  <img src="small.jpg" alt="Example">
</picture>

<img data-src="large.jpg" alt="Example" class="lazyload">

document.addEventListener("DOMContentLoaded", function() {
  var lazyImages = [].slice.call(document.querySelectorAll("img.lazyload"));
  if ("IntersectionObserver" in window) {
    let lazyImageObserver = new IntersectionObserver(function(entries, observer) {
      entries.forEach(function(entry) {
        if (entry.isIntersecting) {
          let lazyImage = entry.target;
          lazyImage.src = lazyImage.dataset.src;
          lazyImage.classList.remove("lazyload");
          lazyImageObserver.unobserve(lazyImage);
        }
      });
    });
    lazyImages.forEach(function(lazyImage) {
      lazyImageObserver.observe(lazyImage);
    });
  }
});