css - Add div next to other centered div -

i want add div right of other div positioned in center. shown in image:

i have html far:

<div id= "top-menu-wrapper">   <div id="top-menu">          </div>   <div id="social">   </div> </div> 

the css:

#header #top-menu {     display           : inline-block;     width             : 764px;     height            : 55px;     margin            : auto;    }  #header #social {     display           : inline-block;     width             : 100px;     height            : 55px;        margin-left       : 25px;  }  #header #top-menu-wrapper {     display           : block;     text-align        : center;     margin-bottom     : 25px; } 

since widths fixed, calculate left offset of each div, , put left margin without using central alignment.

or, if container fluid, center problematic div inside right-floated subcontainer width of

(top container width - central div width) / 2) (that represents remaining space @ right)

you'll make best if use javascript window resize listener recalculate position on every resize event. (although you'd prefer use css only, i'd suggest js best results)