#include <FastLED.h>

#define NUM_LEDS 16
const byte maptable  [NUM_LEDS]= {7,6,5,4,3,2,1,0,0,1,2,3,4,5,6,7};
// const byte maptable [NUM_LEDS]= {7,6,5,4,3,2,1,0,7,6,5,4,3,2,1,0};  

CRGB leds[NUM_LEDS];
CRGB buff[NUM_LEDS/2];

void setup() {
  FastLED.addLeds<WS2812B, 3, GRB>(leds, NUM_LEDS);
}

void loop() {
  fadeToBlackBy(buff, NUM_LEDS, 2);
  double a= millis()/6;
  buff[sin8((byte)a)*(NUM_LEDS/2)/255] = CRGB::Aquamarine; 
  for (int i = 0; i < NUM_LEDS; i++) {
    nblend (leds[i],buff[maptable[i]],16);
  }
  FastLED.show();
}