CSS problem with divs and inline components - css

Question

Imagine a code like this:
.div {
width: 100%;
height: 100px;
background-color: green;
}
.div1 {
width: 100px;
height: 100px;
background-color: red;
}
.div2 {
width: 100px;
height: 100px;
background-color: blue;
}
.main {
background-color: yellow;
}
<div class="main">
<div>
<div class="div"></div>
<div class="div1"></div>
</div>
<div class="div2"></div>
</div>
It will render something like this:
I want that the blue div comes up and stay on the right of the red div. Imagine that I can´t change the divs from where they are, so I need to do it in css. How can I do it?

Answer 1

Without changing the markup, if you set float: left to the red <div> then you could put the blue <div> to its right side
.div {
width: 100%;
height: 100px;
background-color: green;
}
.div1 {
width: 100px;
height: 100px;
background-color: red;
float: left;
}
.div2 {
width: 100px;
height: 100px;
background-color: blue;
display: inline-block;
vertical-align: top;
}
.main {
background-color: yellow;
}
<div class="main">
<div>
<div class="div"></div>
<div class="div1"></div>
</div>
<div class="div2"></div>
</div>

Answer 2

The previous solution which uses float on the red div works well, but here is another possible solution:
Apply position: relative; to the blue div (to be able to move it in relation to its default position) and add top: -100px; left: 100px; to move it up next to the red div:
.div {
width: 100%;
height: 100px;
background-color: green;
}
.div1 {
width: 100px;
height: 100px;
background-color: red;
}
.div2 {
width: 100px;
height: 100px;
background-color: blue;
position: relative;
top: -100px;
left: 100px;
}
.main {
background-color: yellow;
}
<div class="main">
<div>
<div class="div"></div>
<div class="div1"></div>
</div>
<div class="div2"></div>
</div>

Answer 3

This can also be done with the grid CSS. Here I used a named template box and then in the "chatty verbose" CSS I put the positional related for each "block". I added classes to the CSS just for clarity but you could update to your classes.
I added some color and things just for clarity and visual references but kept the "position relate" in separate CSS chunks.
.main {
font-size: 2rem;
display: grid;
grid-template: "box";
background-color: yellow;
}
.main *,
.main::before {
grid-area: box;
}
.green-block {
place-self: start;
}
.red-block {
width: 50%;
place-self: end start;
}
.blue-block {
width: 50%;
place-self: end end;
}
.green-block {
height: 3rem;
background-color: green;
}
.red-block {
height: 3rem;
background-color: red;
}
.blue-block {
background-color: blue;
}
.blue-block,
.green-block,
.red-block {
/* color for clarity and just to super center the text in the blocks */
display: grid;
color: cyan;
font-family: sans-serif;
text-transform: uppercase;
place-items: center;
}
<div class="main">
<div>
<div class="div green-block">green</div>
<div class="div1 red-block">red</div>
</div>
<div class="div2 blue-block">blue</div>
</div>