Move child object within parent

How-to
1

Is it possible to move a child within its parent? I’m using LVGL v7.11.0.

If I have a button and then define a child button, I see the child button is placed slightly lower on the parent and cropped off at the bottom. I want to try to shift the child button so it completely overlaps its parent. Thus, I will only see the child button (in its entirety) and not the parent button. Is it possible to do that?

I am experimenting with the lv_eclipse_sdl_sim project, using the lv_ex_btn_1 example:

void lv_ex_btn_1(void)
{
    lv_obj_t * label;

    lv_obj_t * btn1 = lv_btn_create(lv_scr_act(), NULL);
    lv_obj_align(btn1, NULL, LV_ALIGN_CENTER, 0, 0);
    label = lv_label_create(btn1, NULL);
    lv_label_set_text(label, "Button");

    lv_obj_t *child_btn = lv_btn_create(btn1, NULL);
//  lv_obj_align(child_btn, NULL, LV_ALIGN_CENTER, 0, 0);
    label = lv_label_create(child_btn, NULL);
    lv_label_set_text(label, "Child");
}

I get the following output:
default-child

The lv_obj_align doesn’t seem to do anything.

Interestingly, suppose I change the size of the child button to be half the size of the parent in each dimension, as follows:

void lv_ex_btn_1(void)
{
    lv_obj_t * label;

    lv_obj_t * btn1 = lv_btn_create(lv_scr_act(), NULL);
    lv_obj_align(btn1, NULL, LV_ALIGN_CENTER, 0, 0);
    label = lv_label_create(btn1, NULL);
    lv_label_set_text(label, "Button");

    /* NOTE: default button size appears to be 130 x 43 */
    lv_obj_t *child_btn = lv_btn_create(btn1, NULL);
    lv_obj_set_width(child_btn, 65);
    lv_obj_set_height(child_btn, 22);
    label = lv_label_create(child_btn, NULL);
    lv_label_set_text(label, "Child");
}

Then I get some unexpected output:
shrunk-child

The shrunk child is still stuck to the bottom of the parent, and now it seems that the “Button” label of the parent has been shifted up. Can someone explain this behaviour please? If I try to use lv_obj_align or similar functions to move the now smaller child around in the parent, again there is no effect.