Try this:
.main {
background: tomato;
float: left;
width: 600px;
margin-top: 30px; /* above Layout adjustment */
/* removed overflow: hidden; */
/* use always clearfix method instead */
}
.article_header {
background: SteelBlue;
color: #fff;
position: absolute;
bottom: 100%;
margin-bottom: 10px; /* to neutralize padding of parent container */
left: -10px; /* to neutralize padding of parent container */
padding: 10px; /* to neutralize padding of parent container */
right: -330px; /* to neutralize padding of parent container */
}
.main > article{
position: relative;
}
.aside {
background: cyan;
float: right;
width: 300px;
margin-top: 30px; /* above Layout adjustment */
}
To make adjustments, play with margin property.