conf.py: update deprecated stylesheet API; 'add_stylesheet()' renamed to 'add_css_file()'
conf.py: update deprecated stylesheet API; 'add_stylesheet()' renamed to 'add_css_file()'

adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython