Use tabview, Why occur gap in the top and left

Description

I use tabview , and create a button in coordinate(0,0).
but the button display dont in 0,0,

Code

void test_screens(void)
{
tabview = lv_tabview_create(lv_scr_act(), NULL);
lv_tabview_set_btns_hidden(tabview, true);
lv_tabview_set_sliding(tabview, false);

/* Screen 1 */
lv_obj_t * scr1 = lv_tabview_add_tab(tabview, "scr1");
lv_obj_t * btn = lv_btn_create(scr1, NULL);
	lv_obj_set_pos(btn, 0, 0);
lv_obj_set_user_data(btn, (lv_obj_user_data_t)1); /* Store the next screen ID in user data */
lv_obj_set_event_cb(btn, btn_event_cb);
lv_obj_t * label = lv_label_create(btn, NULL);
lv_label_set_text(label, "Flip to Screen 2");

/* Screen 2 */
lv_obj_t * scr2 = lv_tabview_add_tab(tabview, "scr2");
btn = lv_btn_create(scr2, NULL);
lv_obj_set_user_data(btn, (lv_obj_user_data_t)0); /* Store the next screen ID in user data */
lv_obj_set_event_cb(btn, btn_event_cb);
label = lv_label_create(btn, NULL);
lv_label_set_text(label, "Flip to Screen 1");

}

Please show a screenshot of the issue.

It’s probably related to the padding on the tab page.

i want to learn systematic LVGL,can you give me some suggestions?