Center a button under 3 divs - html

Question

I have 3 divs (colored squares) and a button.
How can I center the button under the divs?
With my current code the button appears in the same line as #squares and it's floating to the left. Thanks for your answers.
#div1 {
background-color: red;
width: 100px;
height: 100px;
margin-right: 10px;
}
#div2 {
background-color: green;
width: 100px;
height: 100px;
margin-right: 10px;
}
#div3 {
background-color: blue;
width: 100px;
height: 100px;
}
#squares {
display: flex;
position: absolute;
margin-left: 35%;
}
#button {
width: 100px;
height: 50px;
clear: both;
}
<div id="squares">
<div id="div1"></div>
<div id="div2"></div>
<div id="div3"></div>
</div>
<div id="button">
<button>Click me!</button>
</div>

Answer 1

Since you're already using flexbox, there are multiple solutions, all of them relatively simple.
Here's one:
Wrap both containers in a parent container.
Add display: flex and flex-direction: column to this new container.
Now you can easily align the squares and the button both vertically and horizontally.
#container {
display: flex;
flex-direction: column;
}
#div1 {
background-color: red;
width: 100px;
height: 100px;
}
#div2 {
background-color: green;
width: 100px;
height: 100px;
margin: 0 10px;
}
#div3 {
background-color: blue;
width: 100px;
height: 100px;
}
#squares {
display: flex;
align-self: center;
margin-bottom: 10px;
}
#button {
align-self: center;
text-align: center;
width: 100px;
height: 50px;
}
<div id="container">
<div id="squares">
<div id="div1"></div>
<div id="div2"></div>
<div id="div3"></div>
</div>
<div id="button">
<button>Click me!</button>
</div>
</div>

Answer 2

Is there a specific reason you are using position: absolute for the square-container?
If not, you can just make the position relative, recenter the content and center the button.
Important code changes:
#squares {
position: relative;
justify-content: center;
}
#button {
margin: 0 auto;
}
Fiddle: https://jsfiddle.net/q17fa25w/

Answer 3

Other way to solve it, you can set padding left and top for #button div like this:
#button {
width: 100px;
height: 50px;
clear: both;
padding: 120px 35%;
}