@mixin linear-background($color1: null, $color2: null, $direction: null) {
    @if $direction != null {
        background-image: linear-gradient(to $direction, $color1, $color2);
    }
}

@mixin linear-percent-background($color1: null, $color2: null, $direction: null) {
    @if $direction != null {
        background-image: linear-gradient(to $direction, $color1 1%, $color2 99%);
    }
}