HTML / CSS: Section + Aside Issue - html

Question

I've an issue with my aside bar and the timestamp in my section.
<section>
<div class="thumbnail-title">
Sample
</div>
<div class="thumbnail-image"></div>
<div class="thumbnail-text">
<div class="thumbnail-timestamp">
02-11-2016 18:51 P.M.
</div>
Hello this is random text that I will test today to see if my sizing is correct.
ello this is random text that I will test today to see if my sizing is correct.
</div>
</section>
<aside>
Random Aside Text.
</aside>
If I add more sections, the aside bar sticks to the last section, where as I want it to stick from top downwards.
Also my timestamp is okay if one section exists but if more sections are added, timestamp get's pushed below the text.
Here is the CSS:
section,
aside
{
margin: 20px 20px 24px 0;
}
section
{
float: left;
width: 55%;
margin-left: 20px;
border: 3px solid black;
padding-bottom: 20px;
border-radius: 10px;
}
.thumbnail-title
{
border: 3px solid black;
border-top: none;
border-left: none;
border-right: none;
padding: 15px;
text-align: center;
font-size: 24px;
margin-bottom: 20px;
}
.thumbnail-image
{
float: left;
height: 200px;
width: 300px;
border: 3px solid black;
margin-left: 20px;
margin-right: 20px;
border-radius: 10px;
}
.thumbnail-text
{
font-size: 18px;
text-align: left;
padding: 20px;
padding-left: 20px;
margin-left: 20px;
margin-right: 20px;
border-radius: 10px;
}
.thumbnail-timestamp
{
border: 1px solid black;
text-align: right;
float: right;
width: 360px;
height: 10px;
padding: 2px;
font-size: 10px;
margin-bottom: 10px;
border-top: none;
border-left: none;
border-right: none;
}
aside
{
float: right;
width: 38%;
padding: 10px;
border: 3px solid black;
border-radius: 10px;
}
I want my page to look like this:
Idea

Answer 1

Be care with margin property. (I mean by that margin: 20px 20px 24px 0; is cool, but it's 'dangerous' when you want inline elements)
Set display: inline-block or play with flexbox (amazing things)
Set correct percentage for your width.
If you set a margin: 20px, it doesn't seem to be big, but in fact, it's huge (especially when you resizing, or when you want to set elements in same line.)
Is this something you want ? http://codepen.io/anon/pen/ZBrYde