how to align absolute child's vertical position to parent div - html

Question

I'm trying to make the child divs (option-info) stay just below the parent div but also give them 100% width.
Now the children are centered and have 100% but aren't positioned relative to the parent div. Is there a way to give the child div absolute width but relative positioning vertically in CSS and HTML? Thanks in advance!
Here's the HTML:
<div id="container">
<div class="option-container">
<div class="header">hardware</div>
<div class="option-info">test</div>
</div>
<div class="option-container">
<div class="header">design</div>
<div class="option-info">test</div>
</div>
<div class="option-container">
<div class="header">software</div>
<div class="option-info">test</div>
</div>
<div class="option-container">
<div class="header">gaming</div>
<div class="option-info">test</div>
</div>
</div>
Here's the CSS:
.header {
display: inline-block;
position: relative;
background-color: rgb(81, 154, 226);
font-size: 2.3em;
height: 100px;
color: white;
font-family: 'saira', arial;
text-shadow: 2px 2px #2280dd;
width: 250px;
text-align: center;
text-transform: uppercase;
margin: auto;
top: 70px;
-webkit-box-shadow: 0px 12px 60px -17px rgba(0,0,0,0.75);
-moz-box-shadow: 0px 12px 60px -17px rgba(0,0,0,0.75);
box-shadow: 0px 12px 60px -17px rgba(0,0,0,0.75);
z-index: 1;
line-height: 100px;
}
#container {
text-align: center;
width: 100%;
}
.option-container {
display: inline-block;
width: 250px;
margin: 22px 22px 100px 22px;
}
.option-info {
display: inline-block;
position: absolute;
width: 100%;
font-family: 'roboto', arial;
font-size: 1.3em;
text-align: center;
right: 0;
left: 0;
}

Answer 1

Would something like this work for you? I took the option-info element out of the HTML and used the :after pseudo to insert the text in the desired (if I understood correctly) location.
.header {
display: inline-block;
position: relative;
background-color: rgb(81, 154, 226);
font-size: 2.3em;
height: 100px;
color: white;
font-family: 'saira', arial;
text-shadow: 2px 2px #2280dd;
width: 250px;
text-align: center;
text-transform: uppercase;
margin: auto;
top: 70px;
-webkit-box-shadow: 0px 12px 60px -17px rgba(0,0,0,0.75);
-moz-box-shadow: 0px 12px 60px -17px rgba(0,0,0,0.75);
box-shadow: 0px 12px 60px -17px rgba(0,0,0,0.75);
z-index: 1;
line-height: 100px;
}
#container {
text-align: center;
width: 100%;
}
.option-container {
display: inline-block;
width: 250px;
margin: 22px 22px 100px 22px;
position: relative;
}
.option-container:after {
width: 100%;
position: absolute;
padding: 10px 0;
content: 'test';
bottom: -120px;
left: 0;
z-index: 9999;
font-family: 'roboto', arial;
font-size: 1.3em;
text-align: center;
}
<div id="container">
<div class="option-container">
<div class="header">hardware</div>
</div>
<div class="option-container">
<div class="header">design</div>
</div>
<div class="option-container">
<div class="header">software</div>
</div>
<div class="option-container">
<div class="header">gaming</div>
</div>
</div>

Answer 2

So I tried restructuring the HTML and this is what I came up with, and this is exactly what I was looking for!
<div class="option-container">
<div class="header">hardware</div>
<div class="info-container">
<div class="option-info">test</div>
</div>
</div>
<div class="option-container">
<div class="header">design</div>
<div class="info-container">
<div class="option-info">test</div>
</div>
</div>
<div class="option-container">
<div class="header">software</div>
<div class="info-container">
<div class="option-info">test</div>
</div>
</div>
<div class="option-container">
<div class="header">gaming</div>
<div class="info-container">
<div class="option-info">test</div>
</div>
</div>
And I just changed two things with the CSS:
.info-container {
position: absolute;
width: 100%;
right: 0;
left: 0;
height: 100%;
}
.option-info {
display: inline-block;
position: relative;
width: 100%;
font-family: 'roboto', arial;
font-size: 1.3em;
text-align: center;
color: black;
color: rgba(0, 0, 0, 0.9);
margin: auto;
top: 100px;
}
EDIT: I appreciate the answers, but it seems I fixed my own problem.