If you want to control the spacing between the two divs that are side by side, put both of the divs in a wrapper div. Float one left and the other right. Set a width for the wrapper div and center it with: margin: 0 auto;
You could remove the float property and set it to display:inline-block; (then add margin-left to the first one to space it out if required.)
It is possible that if the float property is pushing it underneath that maybe there isn't enough space in the wrapper div for the two elements to sit side by side. To test this leave your code as is with the float properties and reduce the width of the second div to see if you can sit it next to it.