One plus 3T - Manual (Page 16)

16 | What’s in the Box Device OxygenOS Safety Information
Customization
OxygenOS features a native dark mode that makes for a pleasant
viewing experience. Change your accent color from the customization
page under settings to express your personal style. OxygenOS also
supports custom icons packs in almost every format, allowing you to
drastically alter the look and feel of your device. Options to fine-tune
the LED indicator, icon grid size and more, are also in place.