Transition background-color via slide animation - css

Question

I am trying to change the background-color of an element on hover by using CSS transitions. I want to do this by having it scroll up from the bottom. I can fade the background in using this, but I would like it to slide up:
-webkit-transition: background-color 0.5s linear;
-moz-transition: background-color 0.5s linear;
-o-transition: background-color 0.5s linear;
transition: background-color 0.5s linear;
One other thought, would it be better to scroll up a separate element with the background applied to it?

Answer 1

In order to slide the background color up you would need to use a background image, or a gradient of some sort, while gradually adjusting the background-position:
.box {
width: 200px; height: 100px;
background-size: 100% 200%;
background-image: linear-gradient(to bottom, red 50%, black 50%);
-webkit-transition: background-position 1s;
-moz-transition: background-position 1s;
transition: background-position 1s;
}
.box:hover {
background-position: 0 -100%;
}
<div class="box"></div>

Answer 2

An extension to #Sampson answer where I will consider more friendly values easier to understand:
.box {
width: 100px;
height: 100px;
display:inline-block;
background-size: 200% 200%;
transition: background-position 1s;
}
.to-top{
background-image: linear-gradient(to top, red 50%, black 0);
background-position: top;
}
.to-top:hover {
background-position: bottom;
}
.to-bottom{
background-image: linear-gradient(to bottom, red 50%, black 0);
background-position: bottom;
}
.to-bottom:hover {
background-position: top;
}
.to-left{
background-image: linear-gradient(to left, red 50%, black 0);
background-position: left;
}
.to-left:hover {
background-position: right;
}
.to-right{
background-image: linear-gradient(to right, red 50%, black 0);
background-position: right;
}
.to-right:hover {
background-position: left;
}
<div class="box to-top"></div>
<div class="box to-bottom"></div>
<div class="box to-left"></div>
<div class="box to-right"></div>
Here is more fancy transitions:
.box {
width: 100px;
height: 100px;
display:inline-block;
transition: 1s;
}
.to-center{
background:
linear-gradient(black,black) no-repeat,
red;
background-size: 100% 100%;
background-position:center;
}
.to-center:hover {
background-size: 0% 100%; /* Or 100% 0% */
}
.from-center{
background:
linear-gradient(red,red) no-repeat,
black;
background-size: 0% 100%; /* Or 100% 0% */
background-position:center;
}
.from-center:hover {
background-size: 100% 100%;
}
.diagonal-right{
background-image:linear-gradient(to bottom right,red 49.5%,black 50%);
background-size: 200% 200%;
background-position:bottom right;
}
.diagonal-right:hover {
background-position:top left;
}
.diagonal-left{
background-image:linear-gradient(to bottom left,red 49.5%,black 50%);
background-size: 200% 200%;
background-position:bottom left;
}
.diagonal-left:hover {
background-position:top right;
}
<div class="box to-center"></div>
<div class="box from-center"></div>
<div class="box diagonal-right"></div>
<div class="box diagonal-left"></div>
Related question to get more details about how background-position works combined with background-size: Using percentage values with background-position on a linear-gradient
Other ideas using circular shapes:
.box {
width: 100px;
height: 100px;
display:inline-block;
transition: 1s;
}
.to-center{
background:
radial-gradient(farthest-side,black 98%,transparent) no-repeat,
red;
background-size: 150% 150%;
background-position:center;
}
.to-center:hover {
background-size: 0% 0%;
}
.from-center{
background:
radial-gradient(farthest-side,red 98%,transparent) no-repeat,
black;
background-size: 0% 0%;
background-position:center;
}
.from-center:hover {
background-size: 150% 150%;
}
.diagonal-right{
background:radial-gradient(farthest-side,red 48%,transparent 50%) no-repeat,
black;
background-size: 300% 300%;
background-position:bottom right;
}
.diagonal-right:hover {
background-position:center;
}
.to-left{
background:radial-gradient(farthest-side,red 48%,transparent 50%) no-repeat,
black;
background-size: 400% 400%;
background-position:left;
}
.to-left:hover {
background-position:center;
}
<div class="box to-center"></div>
<div class="box from-center"></div>
<div class="box diagonal-right"></div>
<div class="box to-left"></div>
Related: How to animate a radial-gradient using CSS?