// 镂空小箭头（IE8及以下浏览器不支持）
._arrow2(@color, @size, @thickness, @position, @margin, @pseudo_elements) {
    @selector: e(':@{pseudo_elements}');
    &@{selector} {
        content: '';
        display: block;
        .size(@size - @thickness);
        .border-top(@color, @thickness);
        .border-left(@color, @thickness);
        .position(@position);
        margin: @margin;
    }
}
.arrow2-color(@color, @pseudo_elements: before) { //仅用于改变箭头颜色
    @selector: e(':@{pseudo_elements}');
    &@{selector} {
        border-color: @color;
    }
}
.arrow2-left(@color, @size, @thickness: 2px, @position: auto, @margin: 0, @pseudo_elements: before) {
    ._arrow2(@color, @size, @thickness, @position, @margin, @pseudo_elements);
    @selector: e(':@{pseudo_elements}');
    &@{selector} {
        .rotate(-45deg);
    }
}
.arrow2-right(@color, @size, @thickness: 2px, @position: auto, @margin: 0, @pseudo_elements: before) {
    ._arrow2(@color, @size, @thickness, @position, @margin, @pseudo_elements);
    @selector: e(':@{pseudo_elements}');
    &@{selector} {
        .rotate(135deg);
    }
}
.arrow2-up(@color, @size, @thickness: 2px, @position: auto, @margin: 0, @pseudo_elements: before) {
    ._arrow2(@color, @size, @thickness, @position, @margin, @pseudo_elements);
    @selector: e(':@{pseudo_elements}');
    &@{selector} {
        .rotate(45deg);
    }
}
.arrow2-down(@color, @size, @thickness: 2px, @position: auto, @margin: 0, @pseudo_elements: before) {
    ._arrow2(@color, @size, @thickness, @position, @margin, @pseudo_elements);
    @selector: e(':@{pseudo_elements}');
    &@{selector} {
        .rotate(-135deg);
    }
}