Try to use flexbox model. It is easy and short to write.
Live Jsfiddle
CSS:
#wrapper {
display: flex;
border: 1px solid black;
}
#first {
border: 1px solid red;
}
#second {
border: 1px solid green;
}
default direction is row. So, it aligns next to each other inside the #wrapper. But it is not supported IE9 or less than that versions