I am limited by the confines of my tools, but these are the layers needed.

Here is the command to generate it fully formed.

!give @p minecraft:red_banner[banner_patterns=[{“pattern”:“minecraft:stripe_center”,“color”:“white”},{“pattern”:“minecraft:rhombus”,“color”:“lime”},{“pattern”:“minecraft:triangles_top”,“color”:“lime”},{“pattern”:“minecraft:guster”,“color”:“pink”},{“pattern”:“minecraft:diagonal_up_left”,“color”:“lime”},{“pattern”:“minecraft:diagonal_up_right”,“color”:“lime”}]]!<