CSS linear gradient progress animation - css

Question

I've put together an animation which indicates a countdown until a toast notification disappears:
.toastDiv {
animation: toastProgress 3s ease;
border: 1px solid rgba(0, 0, 0, .5);
border-radius: 5px;
box-shadow: 0 0 5px 0 rgba(0, 0, 0, .25);
margin: 0 0 1ex 0;
padding: 1ex 1em;
}
#keyframes toastProgress {
0% {
background: linear-gradient(to right, aliceblue 0%, aliceblue 0%, white 0%, white 100%);
}
10% {
background: linear-gradient(to right, aliceblue 0%, aliceblue 10%, white 10%, white 100%);
}
20% {
background: linear-gradient(to right, aliceblue 0%, aliceblue 20%, white 20%, white 100%);
}
30% {
background: linear-gradient(to right, aliceblue 0%, aliceblue 30%, white 30%, white 100%);
}
40% {
background: linear-gradient(to right, aliceblue 0%, aliceblue 40%, white 40%, white 100%);
}
50% {
background: linear-gradient(to right, aliceblue 0%, aliceblue 50%, white 50%, white 100%);
}
60% {
background: linear-gradient(to right, aliceblue 0%, aliceblue 60%, white 60%, white 100%);
}
70% {
background: linear-gradient(to right, aliceblue 0%, aliceblue 70%, white 70%, white 100%);
}
80% {
background: linear-gradient(to right, aliceblue 0%, aliceblue 80%, white 80%, white 100%);
}
90% {
background: linear-gradient(to right, aliceblue 0%, aliceblue 90%, white 90%, white 100%);
}
100% {
background: linear-gradient(to right, aliceblue 0%, aliceblue 100%, white 100%, white 100%);
}
}
<div class="toastDiv">hello</div>
However, it is very tedious to have to spell out the individual animation stages and at the granularity I chose, I am getting choppy results.
I tried using this:
#keyframes toastProgress {
from {
background: linear-gradient(to right, aliceblue 0%, aliceblue 0%, white 0%, white 100%);
}
to {
background: linear-gradient(to right, aliceblue 0%, aliceblue 100%, white 100%, white 100%);
}
}
But this transitions from one solid background to the next instead of animating the color stops from left to right.
Is there a way to make this progress-style gradient animation using only from and to and not percent-steps?

Answer 1

You can rely on background-size animation and steps() like below:
.toastDiv {
border: 1px solid rgba(0, 0, 0, .5);
border-radius: 5px;
box-shadow: 0 0 5px 0 rgba(0, 0, 0, .25);
margin: 0 0 1ex 0;
padding: 1ex 1em;
background:
linear-gradient(aliceblue,aliceblue) left no-repeat,
white;
animation: toastProgress 5s steps(10,start);
}
#keyframes toastProgress {
0% {
background-size:0% 100%;
}
100% {
background-size:100% 100%;
}
}
<div class="toastDiv">hello</div>
<div class="toastDiv" style="animation-timing-function:ease">without Steps</div>
Related to understand how steps() works: https://stackoverflow.com/a/51843473/8620333