Here is an example to make a check box look like a push button:
button := CCheckBox new. button label := 'CheckBox'. button costume := CPushButtonCostume. button open
And while we're at it, here is an example that uses a mixture of push button, radio button and check box costumes for three radio buttons:
button1 := CRadioButton new. button1 label := 'Button1'. button1 costume := CPushButtonCostume. button1 open. button2 := CRadioButton new. button2 label := 'Button2'. button2 costume := CCheckBoxCostume. button2 openAt: button1 bottomLeft. button3 := CRadioButton new. button3 label := 'Button3'. button3 costume := CRadioButtonCostume. button3 openAt: button2 bottomLeft.