CSS Wiping animation on exit - css

Question

I have an animation that wipes from left to right on hover here. I want to have an exit animation that also goes from left to right (not right to left as shown in the demo). How can I achieve this?
.btn {
color: #31302B;
background: #FFF;
margin: 25px;
padding: 10px 0;
width: 240px;
border: 3px solid #31302B;
font-size: 14px;
font-weight: bold;
letter-spacing: 1px;
text-transform: uppercase;
border-radius: 2px;
display: inline-block;
text-align: center;
cursor: pointer;
box-shadow: inset 0 0 0 0 #6a0dad;
-webkit-transition: all ease 0.8s;
-moz-transition: all ease 0.8s;
transition: all ease 0.8s;
}
.btn:hover {
box-shadow: inset 240px 0 0 0 #6a0dad;
color: #fff;
}
<div class="btn">CONTAINER</div>

Answer 1

You could use #keyframes:
.btn {
color: #31302B;
background: #FFF;
margin: 25px;
padding: 10px 0;
width: 240px;
border: 3px solid #31302B;
font-size: 14px;
font-weight: bold;
letter-spacing: 1px;
text-transform: uppercase;
border-radius: 2px;
display: inline-block;
text-align: center;
cursor: pointer;
animation: out 0.8s ease;
}
#keyframes in {
from {
box-shadow: inset 0 0 0 0 #6a0dad;
color: black;
}
to {
box-shadow: inset 240px 0 0 0 #6a0dad;
color: white;
}
}
#keyframes out {
from {
box-shadow: inset -240px 0 0 0 #6a0dad;
color: white;
}
to {
box-shadow: inset 0 0 0 0 #6a0dad;
color: black;
}
}
.btn:hover {
animation: in 0.8s ease;
box-shadow: inset 240px 0 0 0 #6a0dad;
color: white;
}
<div class="btn">CONTAINER</div>

Answer 2

I would suggest using pseudo-element ::after and transform-origin for this.
.btn::after {
z-index: -1;
content: '';
position: absolute;
left: 0;
top: 0;
background: #6a0dad;
height: 100%;
width: 100%;
transform: scaleX(0);
transition: all ease 0.8s;
transform-origin: left;
}
.btn:hover {
color: white;
}
.btn:hover::after {
transform: scaleX(1);
transform-origin: right;
}
Add position: relative; z-index: 1; to .btn class

Answer 3

A simple background transition can easily do this without keyframes:
.btn {
color: #31302B;
background: #FFF;
margin: 25px;
padding: 10px 0;
width: 240px;
border: 3px solid #31302B;
font-size: 14px;
font-weight: bold;
letter-spacing: 1px;
text-transform: uppercase;
border-radius: 2px;
display: inline-block;
text-align: center;
cursor: pointer;
background:linear-gradient(#6a0dad,#6a0dad) left/0% 100% no-repeat;
transition: all ease 0.5s,background-position 0s 0.5s;
}
.btn:hover {
background-size:100% 100%;
background-position:right;
color: #fff;
}
<div class="btn">CONTAINER</div>
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