Keyframe css animation - html

Question

Question
let's if i have the following example
A-------------B------------C
how i can start an animation from the middle ( B ) then it go to A then to B and finaly it go to C , i made an example but it's not working good.
Code
.container {
display: block;
}
.container .line {
display: block;
height: 1px;
width: 400px;
background: red;
}
.line:after{
content: "";
height: 20px;
width: 20px;
display: block;
background: black;
border-radius: 50%;
position: absolute;
left: 200px;
top: 0px;
}
#keyframes move {
0% {
left: 200px;
}
25%{
left: 0px;
}
100%{
left: 400px;
}
}
.line:after {
-webkit-animation: move 1s alternate infinite;
-moz-animation: move 1s alternate infinite;
-ms-animation: move 1s alternate infinite;
-o-animation: move 1s alternate infinite;
animation: move 1s alternate infinite;
}
<div class="container">
<div class="line"></div>
</div>

Answer 1

If you do it this way, I thinks it's working well.
In stead of alternate I did use linear. It makes the animation smoother.
.container {
display: block;
}
.container .line {
display: block;
height: 1px;
width: 400px;
background: red;
}
.line:after{
content: "";
height: 20px;
width: 20px;
display: block;
background: black;
border-radius: 50%;
position: absolute;
left: 200px;
top: 0px;
}
#keyframes move {
0% {
left: 200px;
}
25%{
left: 0px;
}
75%{
left: 400px;
}
100%{
left: 200px;
}
}
.line:after {
-webkit-animation: move linear 1s infinite;
-moz-animation: move linear 1s infinite;
-ms-animation: move linear 1s infinite;
-o-animation: move linear 1s infinite;
animation: move linear 1s infinite;
}
<div class="container">
<div class="line"></div>
</div>

Answer 2

You could do it like this, also if add linear (because default is ease) you will get something like this Fiddle
.container .line {
height: 1px;
width: 400px;
background: red;
}
.line:after{
content: "";
height: 20px;
width: 20px;
background: black;
border-radius: 50%;
position: absolute;
left: 200px;
top: 0px;
animation: move 3s infinite;
}
#keyframes move {
0% {left: 200px;}
25%{left: 0px;}
50% {left: 200px;}
75% {left: 400px;}
100%{left: 200px;}
}
<div class="container">
<div class="line"></div>
</div>