Fillet

Round the corner of 2 objects



Home tab > Modify panel > Fillet



Command line: Radius



Specify fillet radius: 200



Select 1st object



Select 2nd object



Repeat the same steps on the right corner



Start Fillet command
Command line: Trim



Select No trim



Command line: Polyline



Select the aquare



Start Fillet command
Select the top line


Select the bottom line