Centering div in CSS (WP theme development and PHP) - php

Question

I'm currently developing a wordpress theme with PHP, but my problem is with the css. I have tree divs, which i have inside a parent div. The parents div is by default 100%, so i want to specify the parent div (class: "single-general-sec1"). I've tried to calculate how wide the parent div should be in order for me to center it, but my calculations do not work. Please help.
Parent div should, by my calculation, be: 61% + 425px, but that dosen't work.
.single-general-sec1 {
margin-top: 150px;
margin-bottom: 150px;
height: auto;
width: calc(61% + 425px);
background-color: red;
}
.single-btype-div {
width: 250px;
display: inline-block;
float: left;
}
.single-gen-header {
font-size: 14px;
color: #D9D9D9;
font-family: "Roboto";
font-weight: 700;
text-transform: uppercase;
letter-spacing: 3px;
margin: 0;
width: auto;
}
.single-gen-desc {
color: #000;
font-family: "Roboto";
font-size: 28px;
font-weight: 300;
letter-spacing: 3px;
margin: 0;
width: auto;
margin-top: 5px;
}
.single-description-div {
width: 55%;
display: inline-block;
margin-left: 3%;
float: left;
}
.single-description-desc {
color: #000;
font-family: "Roboto";
font-size: 20px;
font-weight: 300;
letter-spacing: 1px;
margin: 0;
width: auto;
margin-top: 5px;
}
.single-live-button {
margin-top: 5px;
width: 175px;
height: 40px;
background-color: #8AA6B6;
border-radius: 8px;
border: none;
color: #fff;
font-size: 15px;
font-family: "Roboto";
font-weight: 300;
letter-spacing: 2px;
text-transform: uppercase;
}
.single-live-div {
width: 100px;
display: inline-block;
margin-left: 3%;
}
<div class="single-general-sec1">
<div class="single-btype-div">
<p class="single-gen-header"> - Typ av projekt </p>
<p class="single-gen-desc">
<?php the_field('project-type'); ?> </p>
</div>
<div class="single-description-div">
<p class="single-gen-header"> - Beskrivning </p>
<p class="single-description-desc">
<?php the_field('description'); ?> </p>
</div>
<div class="single-live-div">
<p class="single-gen-header"> - Se live </p>
<a href="<?php the_field('page-url') ?>"><button class="single-live-button">
Besök sida > </button></a>
</div>
</div>

Answer 1

You cannot center a div using % values for width. Also the calculation is wrong: 250px + 175px + 100px = 525px so, the parent div should be 525px in order to fit nested divs. But you should normalize HTML first. Or just use bootstrap.css.
Another thing. For center a div you can use display:inline-block then on his parent use text-align:center.
Or when you have a fixed width, margin:50px auto;