@mixin button-linear($shadow, $color, $colorDark) {
    background: -moz-linear-gradient(top, $color 0%, $colorDark 100%);
    background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, $color), color-stop(100%, $colorDark));
    background: -webkit-linear-gradient(top, $color 0%, $colorDark 100%);
    background: -o-linear-gradient(top, $color 0%, $colorDark 100%);
    background: -ms-linear-gradient(top, $color 0%, $colorDark 100%);
    background: linear-gradient(top, $color 0%, $colorDark 100%);
    text-shadow: 0px 1px 1px $shadow;
    filter: dropshadow(color=$shadow, offx=0, offy=1);
}
