Only CSS rotate box-shadow without original element

问题

I have a small problem, I want to create 45 degree shadow for a picture. But if I use my code my object is rotating too. So I would like to ask for help with this problem.

My code:

.item {
    box-shadow: -50px 80px 4px 10px #555;
    -webkit-transform: rotate(10deg);
    -moz-transform: rotate(10deg);
    -o-transform: rotate(10deg);
    -ms-transform: rotate(10deg);
    transform: rotate(10deg);
}

回答1:

Most flexible answer using only CSS is probably this:

.item {
    position: relative; /* or absolute */
}

.item:before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: transparent;

    box-shadow: -50px 80px 4px 10px #555;
    -webkit-transform: rotate(10deg);
    -moz-transform: rotate(10deg);
    -o-transform: rotate(10deg);
    -ms-transform: rotate(10deg);
    transform: rotate(10deg);
}

回答2:

You can do it using peudo-element (I've used arbitrary values, you need to tweak it yourself) :

.item {
  margin-left: 50%;
  position: relative;
  width: 100px;
  height: 100px;
  background-color: red;
}
.item:before {
  z-index: -1;
  position: absolute;
  content: "";
  display: block;
  width: 100px;
  height: 100px;
  top: -30px;
  left: 0;
  background-color: transparent;
  box-shadow: -50px 120px 4px 10px #555;
  -webkit-transform: rotate(10deg);
  -moz-transform: rotate(10deg);
  -o-transform: rotate(10deg);
  -ms-transform: rotate(10deg);
  transform: rotate(10deg);
}

<div class="item"></div>

来源：https://stackoverflow.com/questions/31941277/only-css-rotate-box-shadow-without-original-element