This unit will turn pink as soon as it will be less than the width of 600px
This unit turns orange as soon as it becomes more width 900px
This block will be blue if its width is more than 600px and 900px
This unit will only change for the devices max-device-width: 480px (for example iPhone)

You're viewing area: less then 600px between 600 - 900px wider than 900px