postal/app/assets/stylesheets/application/elements/_button.scss

.button {
  display:inline-block;
  font:inherit;
  border-radius:4px;
  appearance:none;
  background:$blue;
  color:#fff;
  font-size:14px !important;
  margin:0;
  vertical-align:top;
  padding:6px 15px;
  border:2px solid transparent;
  border-bottom:2px solid darken($blue, 20%);
  &:active {
    background-color:darken($blue, 15%);
  }
  &:focus {
    border-color:darken($blue, 15%);
    background-color:lighten($blue, 5%);
  }
  &.is-spinning {
    color:transparent;
    background-repeat:no-repeat;
    background-position: center center;
    background-size:25px;
    background-image:image-url('button-spinner.gif');
  }
}

.button--small {
  font-size:12px !important;
  padding:3px 10px;
  border-width:1px;
}

.button--positive {
  background-color:$green;
  border-bottom-color:darken($green, 15%);
  &:active {
    background-color:darken($green, 15%);
  }
  &:focus {
    border-color:darken($green, 15%);
    background-color:lighten($green, 5%);
  }
  &.is-spinning {
    background-image:image-url('button-spinner-positive.gif');
  }

}


.button--neutral {
  background-color:#ccc;
  border-bottom-color:darken(#ccc, 15%);
  &:active {
    background-color:darken(#ccc, 15%);
  }
  &:focus {
    border-color:darken(#ccc, 15%);
    background-color:lighten(#ccc, 5%);
  }
  &.is-spinning {
    background-image:image-url('button-spinner-neutral.gif');
  }
}

.button--danger {
  background-color:$red;
  border-bottom-color:darken($red, 15%);
  &:active {
    background-color:darken($red, 15%);
  }
  &:focus {
    border-color:darken($red, 15%);
    background-color:lighten($red, 5%);
  }
  &.is-spinning {
    background-image:image-url('button-spinner-danger.gif');
  }
}

.button--dark {
  background-color:$darkBlue;
  border-bottom-color:darken($darkBlue, 15%);
  &:active {
    background-color:darken($darkBlue, 15%);
  }
  &:focus {
    border-color:darken($darkBlue, 15%);
    background-color:lighten($darkBlue, 5%);
  }
  &.is-spinning {
    background-image:image-url('button-spinner-dark.gif');
  }

}