// 三角
.triangle(top, @color, @width, @height: @width) {
    @width_half: @width * .5;
    .size(0);
    .border-bottom(@color, @height);
    .border-left(transparent, @width_half);
    .border-right(transparent, @width_half);
}
.triangle(bottom, @color, @width, @height: @width) {
    @width_half: @width * .5;
    .size(0);
    .border-top(@color, @height);
    .border-left(transparent, @width_half);
    .border-right(transparent, @width_half);
}
.triangle(left, @color, @width, @height: @width) {
    @height_half: @height * .5;
    .size(0);
    .border-right(@color, @width);
    .border-top(transparent, @height_half);
    .border-bottom(transparent, @height_half);
}
.triangle(right, @color, @width, @height: @width) {
    @height_half: @height * .5;
    .size(0);
    .border-left(@color, @width);
    .border-top(transparent, @height_half);
    .border-bottom(transparent, @height_half);
}
.triangle(top-left, @color, @width, @height: @width) {
    @width_half: @width * .5;
    @height_half: @height * .5;
    .size(0);
    .border-top(@color, @height_half);
    .border-left(@color, @width_half);
    .border-bottom(transparent, @height_half);
    .border-right(transparent, @width_half);
}
.triangle(top-right, @color, @width, @height: @width) {
    @width_half: @width * .5;
    @height_half: @height * .5;
    .size(0);
    .border-top(@color, @height_half);
    .border-left(transparent, @width_half);
    .border-bottom(transparent, @height_half);
    .border-right(@color, @width_half);
}
.triangle(bottom-left, @color, @width, @height: @width) {
    @width_half: @width * .5;
    @height_half: @height * .5;
    .size(0);
    .border-top(transparent, @height_half);
    .border-left(@color, @width_half);
    .border-bottom(@color, @height_half);
    .border-right(transparent, @width_half);
}
.triangle(bottom-right, @color, @width, @height: @width) {
    @width_half: @width * .5;
    @height_half: @height * .5;
    .size(0);
    .border-top(transparent, @height_half);
    .border-left(transparent, @width_half);
    .border-bottom(@color, @height_half);
    .border-right(@color, @width_half);
}