Making this CSS3 animate rotation only rotate once

Question

I'm attempting to animate a pie chart that rotates from 0 degrees to whatever degree I want it to end on (lets say 300 degrees, doesn't matter). There's an underlying circle with one that rotates on top. As it stands right now, the pie chart rotates a full 360 degrees before ending with the final degree position (300 in this case). Right now it only works in Chrome.

JSFiddle

My HTML:

<div class="spinner">
  <span><em></em></span>
  <span><em></em></span>
</div>

My CSS:

.spinner {
  width: 250px;
  height: 250px;
  background: #aaa;
  margin: 0 auto;
  position: relative;
}
.spinner:after {
  position: absolute;
  content: "";
  width: 0%;
  height: 0%;
  border-radius: 100%;
  background: #fff;
  top: 10%;
  left: 10%;
}
.spinner span em {
  background: #0e728e;
  -webkit-animation-duration: 6s; 
}
@-webkit-keyframes rotate-rt {
  0%   { -webkit-transform: rotate(0deg); }
  25%  { -webkit-transform: rotate(180deg); }
  100% { -webkit-transform: rotate(180deg); }
}
@-webkit-keyframes rotate-lt {
  0%   { -webkit-transform: rotate(0deg); }
  25%  { -webkit-transform: rotate(0deg); }
  50%  { -webkit-transform: rotate(120deg); }
  100% { -webkit-transform: rotate(120deg); }
}
.spinner {
  border-radius: 100%;
  position: relative;
}
.spinner span {
  width: 50%;
  height: 100%;
  overflow: hidden;
  position: absolute;
}
.spinner span:first-child {
  left: 0;
}
.spinner span:last-child {
  left: 50%;
}
.spinner span em {
  border-radius: 250px;
  position: absolute;
  width: 100%;
  height: 100%;
  -webkit-animation-iteration-count: 1;
  -webkit-animation-timing-function: linear;
  -webkit-animation-fill-mode: forwards;
}
.spinner span:first-child em {
  left: 100%;
  border-top-left-radius: 0;
  border-bottom-left-radius: 0;
  -webkit-animation-name: rotate-lt; 
  -webkit-transform-origin: 0 50%;
}
.spinner span:last-child em {
  left: -100%;
  border-top-right-radius: 0;
  border-bottom-right-radius: 0;
  -webkit-animation-name: rotate-rt; 
  -webkit-transform-origin: 100% 50%;
 }

Answer 1

This was a little tricky because there are really two circles rotating here. You actually want one (rotate-rt) to stop halfway and the other (rotate-lt) to continue the remaining 120 degrees (300 degrees total):

@-webkit-keyframes rotate-rt {
    0% { -webkit-transform: rotate(0deg); }
   25% { -webkit-transform: rotate(180deg); }
  100% { -webkit-transform: rotate(180deg); }
}
@-webkit-keyframes rotate-lt {
    0% { -webkit-transform: rotate(0deg); }
   25% { -webkit-transform: rotate(0deg); }
   50% { -webkit-transform: rotate(120deg); }
  100% { -webkit-transform: rotate(120deg); }
}

http://jsfiddle.net/BkJY7/7/

Edit: To clarify, if you wanted this to rotate less than 180 degrees, you would remove the second animation keyframes rule altogether: http://jsfiddle.net/BkJY7/8/

Answer 2

You're looking for -webkit-animation-fill-mode: forwards; which stops the animation at the end. You can read more about it here: Can't stop animation at end of one cycle