有没有办法使用 CSS 使背景图像表现得像“封面”但 120%？

Question

CSS 值background-size: cover 将拉伸图像但保持其宽高比。但是，它只会拉伸它，直到最小边达到父节点同一边的 100%。

/* This is an image of 100px Wide x 50px Tall, so it'll 
   stretch to 100% of the window height and then scale the
   width larger to retain its width-to-height ratio.
 */
body
{
    background-image: url( "/images/test.png" );
    background-size: cover;
    background-position: center;
}

我想要一些可以做掩护但比例更大的东西，例如 130%。 （我将在 CSS 关键帧动画中使用它来使背景图像放大/缩小）

我该怎么做？

Answer 1

通过使用伪元素，您可以实现类似的效果

CSS 动画的浏览器支持率为 +90%：http://caniuse.com/#feat=css-animation

.bkg {
  position: absolute;
  left: 0;
  top: 0;
  right: 0;
  bottom: 0;
  overflow: hidden;
}
.bkg::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  background-image: url(http://lorempixel.com/500/400/nature/1);
  background-size: cover;
  background-position: center;
  animation: growme 5s forwards;
}
@keyframes growme {
  from {transform: scale(1);}
  to   {transform: scale(1.3);}  
}

<div class="bkg"></div>

增长和缩小

.bkg {
  position: absolute;
  left: 0;
  top: 0;
  right: 0;
  bottom: 0;
  overflow: hidden;
}
.bkg::before {
  content: '';
  position: absolute;
  left: -20%;
  top: -20%;
  width: 140%;
  height: 140%;
  background-image: url(http://lorempixel.com/500/400/nature/1);
  background-size: cover;
  background-position: center;
  animation: shrinkme ease-in-out 10s infinite;
}
@keyframes shrinkme {
  0%   {transform: scale(1);}
  50%  {transform: scale(.72);}  
  100% {transform: scale(1);}
}

<div class="bkg"></div>

根据一些浏览器存在动画伪元素问题的评论进行更新，其中只需使用子元素即可。

.bkg {
  position: absolute;
  left: 0;
  top: 0;
  right: 0;
  bottom: 0;
  overflow: hidden;
}
.bkg div {
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  background-image: url(http://lorempixel.com/500/400/nature/1);
  background-size: cover;
  background-position: center;
  animation: growme 5s forwards;
}
@keyframes growme {
  from {transform: scale(1);}
  to   {transform: scale(1.3);}  
}

<div class="bkg"><div></div></div>

Answer 2

我之前通过将背景图像应用于绝对定位的伪元素（例如 ::before）并对其应用缩放变换来完成此操作。