func NewBox(uis ...UI) *Box {
	kids := make([]*Kid, len(uis))
	for i, ui := range uis {
		kids[i] = &Kid{UI: ui}
	}
	return &Box{Kids: kids}
}
NewBox returns a box containing all uis in its Kids field.
package duit
import (
	"image"
	"9fans.net/go/draw"
)