How to change the bar style

Hello everyone.
I am using this cool library.
How could I change the bar color from light to dark ?
I want to change the bar progress color form light green to dark green gradually.
The results like this: imgur com/x1mnZ0k

// here is the code I used
bar1 = lv_bar_create(lv_disp_get_scr_act(NULL), NULL);
lv_obj_set_size(bar1, 820, 10);
lv_obj_align(bar1, NULL, LV_ALIGN_IN_TOP_LEFT, -10, 0);
lv_bar_set_anim_time(bar1, 20000);
lv_bar_set_value(bar1, 100, LV_ANIM_ON);
lv_obj_set_style_local_bg_color(bar1,LV_BAR_PART_INDIC , LV_STATE_DEFAULT, LV_COLOR_GREEN);