How to write code for such a background?

Question

css

How to write code for a background that consists of 3 blocks?
(Code I wrote)
.div{
display : inline-block;
width : 640px
height: 720px;
margin : 0px;
}
#one{
background : #c2e6f2
}
.div{
display : inline-block;
width : 640px
height: 360px;
margin : 0px
}
#two
background : #3d6a9e;
}
.div{
display : inline-block;
width : 640px
height : 360px;
margin : 0px
}
#three{
background : #4c846f
}
.div{
display : inline-block;
width : 640px
height : 360px;
margin : 0px
}
Are there any mistakes here?
Thanks in advance for your replies.

Answer 1

why is the .div repeated?

Answer 2

Usually, html is written first - the structure (if that is what is meant by the word "code"), and then styles are added. Especially at the initial level of knowledge.