These are simple bookmarks to put inside your books. these work really well for me.

they have an indent on the top to write stuff in ( or put paper / sticky labels inside (10l x 18w x 1h ))

i printed mine ( the ones in the photos ) in white PLA+ from creality on a modded ender 3 pro 1 with custom firmware, but basically all FDM printers should be able to print these well.

i printed mine without a raft, and used a skirt. 
Settings:
Hotend temp : 205c 

Hotbed temp : 63c

Infill density : 10%

Infill pattern : Gyroid ( on cura )

Print speed : 100mm/s

i provided my GCODE files for the ender 3 so this should work on your ender 3 if you have one. 

both took around 40m to print in one file