CSS-Animation: Border bottom filling from left to right green line.

element.html

<div>
  <input class="dollar-value" type="text" />
  <span class="animation-border"></span>
</div>

style.scss

// Need 'Bourbon' for includes
$green: #00d246;
$grey: #989c9f;

.dollar {
        position: absolute;
        color: $green;
        font-size: 18px;
        font-weight: 400;
        left: 58px
      }

      .dollar-value {
        border: none;
        font-size: 18px;
        border-bottom: 2px solid $grey;
        width: 221px;
        border-radius: 1px;
        padding-left: 30px;
        margin-left: 50px;

        &:focus {
          outline: 0;
        }

        &:focus + .animation-border {
          @include animation-name(green-line-focus);
          @include animation-duration(.5s);
          @include animation-timing-function(ease-in-out);
          @include animation-fill-mode(forwards);
        }
      }
      
    @include keyframes(green-line-focus) {
      from {
        padding-left: 0;
        width: 0;
      }
      to {
        padding-left: 30px;
        width: 221px;
      }
    }