CSS如何实现圆弧和扇形的加载动画

.arc(@direction,@style){
@color:~`"@{style}".split(/,\s+/)[1]`;
@width:~`"@{style}".split(/,\s+/)[0].replace("[","")`;
@shape:~`"@{style}".split(/,\s+/)[2].replace("]","")`;
border: @width transparent @shape;
@length:length(@direction);
.setStyle(@length,@style,@direction);
border-radius: 50%;

.setStyle(@length,@style,@direction) when (@length>0){
@index:@length - 1;
@pos:extract(@direction,@length);
border-@{pos}:@style ;
.setStyle(@index,@style,@direction);

}
}
//使用方式:
@driection 可以是top、left、right、bottom中的一个或多个
@style 需要严格按照 7px solid red 这样的顺序
.arc(left,7px solid red);
.arc(left top,7px solid red);