@shape, @rectangle and @polygon

[Mouvedia]

@shape
    x: <number>;
    y: <number>;
    width: <number> | content;
    height: <number> | content;
    @rectangle
               [<number>]
               top: @corner | [<number>];
               bottom: @corner | [<number>];
               left: @corner | [<number>];
               right: @corner | [<number>];
               topLeft: @corner | [<number>]; (1)
               topRight: @corner | [<number>]; (2)
               bottomLeft: @corner | [<number>]; (3)
               bottomRight: @corner | [<number>]; (4)
                            @corner
                                           size: <number>; (1)
                                           type: (round) | bevel | straight; (2)
               corners:
                            [<number>]
                            (@round)
                                           corners: <number>, <number>, <number>, <number>;
                                           top: <number>;
                                           bottom: <number>;
                                           left: <number>;
                                           right: <number>;
                                           topLeft: <number>; (1)
                                           topRight: <number>; (2)
                                           bottomLeft: <number>; (3)
                                           bottomRight: <number>; (4)
                            @bevel
                                           corners: <number>, <number>, <number>, <number>;
                                           top: <number>;
                                           bottom: <number>;
                                           left: <number>;
                                           right: <number>;
                                           topLeft: <number>;
                                           topRight: <number>;
                                           bottomLeft: <number>;
                                           bottomRight: <number>;
                            @straight
                                           corners: <number>, <number>, <number>, <number>;¹
                                           top: <number>;¹
                                           bottom: <number>;¹
                                           left: <number>;¹
                                           right: <number>;¹
                                           topLeft: <number>¹
                                           topRight: <number>;¹
                                           bottomLeft: <number>;¹
                                           bottomRight: <number>;¹
    @polygon
               sides: <N>;
               angle: -360–360;
               corners:
                            (@straight)
                                           corners: <number>, …;¹
                            @round
                                           corners: <number>, …;
                            @bevel
                                           corners: <number>, …;

¹negative numbers or 0

The default object type of the corners property of @rectangle is round but the default value of the corners property of @rectangle is @straight. In short if you use @ on corners it's @round.

shape: @rectangle;
//is equivalent to
shape: @rectangle { corners: @straight; };

shape: @rectangle { corners: @{ } };
//is equivalent to
shape: @rectangle { corners: @round { } };