How can i set shape for placeholder?

[Dave-Redbrick]

I want to make rect to roundRect but i doesn't affect at all.

        // ...
        placeholder: {
          options: {
            name: "subTitle",
            type: "body",
            x: "25%",
            y: "37%",
            w: "50%",
            h: "10%",
            shape: "roundRect",
            fill: {
              color: "#ffcf90",
            },
            line: {
              color: "000000",
              width: 1,
            },
            align: "center",
            fontSize: 14,
            rectRadius: 20,
          },
          text: "text",
        },