CSS3 Box-Shadow Linear Gradient?
Late to the party, but maybe someone will find it useful! You can actually do it with multiple shadows on the box-shadow:
box-shadow: inset 0px 33px 25px 0 #000,
inset 0 66px 15px 0px #ccc,
inset 0 99px 5px 0px #fff;
codepen example : https://codepen.io/InFecT3D/pen/JQdmeL
Side note: it might be a little "hacky" approach, but in some cases it helps.
Take a look at this video by Lea Verou. The section I linked to talks about something very similar, where you use background-image gradients to make something like a box-shadow. If I can figure out a good working example I'll post an answer, but this should give you a good place to start. You can also do some really cool stuff, like a box shadow curl with the :after pseudo-class to make a shadow appear.
Here are a few simple examples at the top and bottom of a box, and underlining some text. You'll have to play around with it (a lot, probably) to get it to look how you want, but css has some really awesome features (and there will be more and more).
body {
display: flex;
height: 100vh;
width: 100vw;
padding: 0;
margin: 0;
}
.container {
flex: 1;
display: flex;
justify-content: center;
align-items: center;
background:
radial-gradient(at 50% 0, black, transparent 70%),
linear-gradient(0deg, black, transparent 50%) bottom;
background-size: 100% 15px;
background-repeat: no-repeat;
}
.underline {
width: 6em;
text-align:center;
font-size:30px;
}
.underline:after {
content: '\00a0';
background-image:
radial-gradient(at 50% 0, blue 0%, red 50%, transparent 75%);
background-size: 100% 2px;
background-repeat: no-repeat;
float:left;
width:100%;
}<div class="container">
<div class="underline">Hello, world!</div>
</div>To create a rainbow gradient box shadow:
.innerSquare {
background-color: white;
border-radius: 5px;
height: 100%;
width: 100%;
}
.rainbowGradient {
display: flex;
align-items: center;
justify-content: center;
padding: 18px;
border-radius: 5px;
box-shadow: inset 0 0 12px 12px white, inset 0 0 3px 2px white;
background: linear-gradient(to right, orange , yellow, green, cyan, blue, violet);
}<div class="rainbowGradient">
<div class="innerSquare">
<h1>Hello World!</h1>
</div>
</div>