How to set arc backgroud opacity to 0


I want to create 6 circle at same center. But I found ,the background can not be setted to 0.
I created circle by arc.

What MCU/Processor/Board and compiler are you using?

visual studio 2019

What LVGL version are you using?


What do you want to achieve?

make arc background opacity to 0.

What have you tried so far?

test many functions ,like lv_obj_set_style_xx_opa.

Code to reproduce

Add a code snippet which can run in the simulator. It should contain only the relevant code that compiles without errors when separated from your main code base.

The code block(s) should be formatted like:

lv_obj_t* arc[6];
void lv_arc_NEunits_net(op_ui_tydef* ui, lv_obj_t* par, u16 size, u16 v)
    uint8_t i = 1;
    for (i = 0;i< 6;i++)
        arc[i] = lv_arc_create(par);
        lv_arc_set_rotation(arc[i], 0);
        lv_arc_set_value(arc[i], 360);
        lv_arc_set_bg_angles(arc[i], 0, 360);
        lv_obj_remove_style(arc[i], NULL, LV_PART_KNOB);   /*Be sure the knob is not displayed*/
        lv_obj_set_style_arc_width(arc[i], 3, LV_PART_INDICATOR);
        lv_obj_set_style_size(arc[i], lv_pct(10+i*10), LV_PART_MAIN);
        //lv_obj_set_style_size(arc[i], 3, LV_PART_INDICATOR);

        lv_obj_set_style_bg_color(arc[i], lv_palette_main(LV_PALETTE_DEEP_PURPLE), LV_PART_INDICATOR );
        //lv_obj_set_style_border_color(arc[i], lv_palette_main(LV_PALETTE_DEEP_PURPLE), LV_PART_INDICATOR );
        //lv_obj_set_style_outline_color(arc[i], lv_palette_main(LV_PALETTE_DEEP_PURPLE), LV_PART_INDICATOR );
        lv_obj_set_style_bg_opa(arc[i], LV_OPA_TRANSP, LV_PART_MAIN);
        lv_obj_set_style_bg_opa(arc[i], LV_OPA_TRANSP, LV_PART_INDICATOR);
        lv_obj_set_style_bg_img_opa(arc[i], LV_OPA_TRANSP, LV_PART_MAIN);
        lv_obj_set_style_bg_img_recolor_opa(arc[i], LV_OPA_TRANSP, LV_PART_MAIN);
        lv_obj_set_style_img_opa(arc[i], LV_OPA_TRANSP, LV_PART_MAIN);
        lv_obj_set_style_shadow_opa(arc[i], LV_OPA_TRANSP, LV_PART_MAIN);
        //lv_obj_set_style_outline_opa(arc[i], 0, LV_PART_MAIN);
        //lv_obj_set_style_border_opa(arc[i], 0, LV_PART_MAIN);      

Screenshot and/or video

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