html
HTML is the structure. This is not meant for human beings, this is a metaphor for the computer. So, we are not able to see and touch. We seem meaningless. However, the benefits that we are currently undergoing, this metaphor is brought.
css
This is intended to describe the format. This is mainly intended for humans. So, what should be strictly defined, may be redundant. css is determined to be accurate. Must be meant to satisfy the desire for humans. Like to print.