Perspective Shadow with CSS

Question

I have a 950x350 pixel div and would like to create a perspective (and blurred) shadow as shown in the code below (run in full screen):

#slider{
   width: 950px;
   height: 350px;
   background: blue;
   position: relative;
}

#slider img{
   width: 962px;
   height: 31px;
   position: absolute;
   left: -6px;
   bottom: 0px;
}

<div id="slider">
   <img src="https://i.stack.imgur.com/OGKsw.png">
</div>

I did creating an image in Photoshop and placing it below the div, but I would not use image for this, would be 1 request less. It is possible and how to get this effect using HTML/CSS?

Answer 1

Here is a version with 3D Transform:

#slider{
  position:relative;
    width: 300px;
    height: 150px;
    background: blue;
    position: relative;
}

#slider:after {
  display:block;content:"";
  position:absolute;
  width:100%;height:30px;
  top:135px;
  border-radius:5px;
  transform: perspective(10px) translateZ(-2.5px) rotateX(5deg);
  background:#666;
  box-shadow:0 0 10px 10px #666;
  z-index:-1;
}

<div id="slider"></div>

Basically we take the after and rotate it with rotateX. The values I "kicked" quickly just to demonstrate the technique, but trying to individually change each one, gives you a good sense of how it works.

Answer 2

Option 1

Option using shadow on an element ::after, one rotateX() to tip the shadow and a filter:blur to make the element look shaded.

#slider{
    width: 950px;
    height: 350px;
    position: relative;
    perspective: 300px;
}
#slider::after{
    content: "";
    position: absolute;
    width: 950px;
    height: 350px;
    background: blue;
    top: 0;
    left: 0;
    z-index: 1;
}
#slider::before{
    content: "";
    background: rgba(0, 0, 0, 0.5);
    width: 90%;
    height: 40px;
    position: absolute;
    bottom: -20px;
    right: 0;
    left: 0;
    margin: auto;
    border-radius: 5px;
    filter: blur(5px);
    z-index: -1;
    transform: rotateX(45deg);
}

<div id="slider"></div>

---

Option 2

It is also possible using a negative value for the fourth Box-shadow attribute (qurto value is known as the spread ). https://developer.mozilla.org/en-US/docs/Web/CSS/box-shadow

You can adjust these values until you get one that you like, but remember that the fourth value should always be negative to have the effect you want

#slider{
    width: 950px;
    height: 350px;
    background: blue;
    position: relative;
    box-shadow: 0 40px 20px -20px rgba(0, 0, 0, 0.5);
}

<div id="slider"></div>