89. Circular Buffer-I

A developer implements push for a UART receive buffer of size 8:

void push(CircularBuffer *cb, uint8_t data) {
   if (cb->count == cb->capacity) return;
   cb->buffer[cb->head] = data;
   cb->head++;
   cb->count++;
}

After pushing 8 values (filling the buffer), popping 4, and then pushing 1 more — what happens?