Button Style Card Layout

Hi 

Need some one help!!

I want to create a button style card layout.I cannot change  outer line color .How can i change outline color

 a!columnsLayout(
            columns: {
              a!columnLayout(
                contents: {
                  a!cardLayout(
                    contents: a!richTextDisplayField(
                      value: {
                        a!richTextItem(
                          text: "Back",
                          color: "ACCENT",
                          style: "STRONG"
                         
                        )
                      },
                      
                      align: "CENTER",
                      marginAbove: "NONE",
                      marginBelow: "EVEN_LESS"
                    ),
                    link: a!dynamicLink(
                      value: "ACCEPT"
                      /*saveInto: local!acceptTask,*/
                      /*showWhen: count(tointeger(local!selected)) <= 50*/
                    )
                    
                    /*style: "INFO"*/
                  )
                }
              ),
              a!columnLayout(
                contents: {}
              ),
              a!columnLayout(
                contents: {}
              )
            }
          )

My desire image is below.