Custom panel/section link styling in customizer

Yes, it’s possible to change the color and other CSS properties of a section and panel title/link. You just have to figure the CSS selector. Here’s the selector pattern for section and panel.

#accordion-section-SECTION_ID_GOES_HERE .accordion-section-title {
    /* add CSS properties here */
}

#accordion-panel-PANEL_ID_GOES_HERE .accordion-section-title {
    /* add CSS properties here */
}

Say, you have a panel example_panel and a section example_section then the selectors will be like the following –

#accordion-section-example_section .accordion-section-title {
    background-color: tomato;
    border-left-color: tomato;
    color: #fff;
}

#accordion-panel-example_panel .accordion-section-title {
    background-color: purple;
    border-left-color: purple;
    color: #fff;
}

Now if you save your custom CSS in a stylesheet customize-control.css and want to enqueue that then you have to use customize_controls_enqueue_scripts.