hi,
the making of:)

1) extrude 1 rectangle and draw 2 rectangles on surface

2) select the box and do substract boolean with the blue

3) 4 lines to join vertex and mirror them with cyan line

4) 4 lines to join vertex and mirror them with orange line

5) select all lines (16) and do mutual trim with solid

6) select 4 magenta face

7) extrude these (in one operation) with tapered (angle = 20) and flip options

8) subdivise (slider at 67)

9) rotation copy