css - Expand div horizontally & keep right -

i coding 2 column layout, (980px width in total) have background of each div in columns expanding way left/right side, see screenshot.

so on left have blue div width: 49%, inside div text, should expand 470px (to keep text aligned in overall max-width: 980px div), , scale down when viewport getting smaller (screenshot).

is there way of keeping div expanded on screenshots photoshop aligned right in parent, blue div? getting float:right , max-width: 470px this :(

so basically, want right-align div inside blue div. use :

html

<div id="someid">     <p>some text here</p> </div> 

css:

#someid {   margin-left : auto;   margin-right : 0; }