This example demonstrates an OpenLayers map in a fluid layout using Bootstrap CSS.
Note that the OpenLayers stylesheet is loaded before Bootstrap. The Bootstrap CSS sets the maximum width for images to be 100% (of their containing element).
img {
    max-width: 100%;
}
                    This causes problems for images that you might want to be
                    bigger than their containing element (e.g. big tile in small
                    map viewport).  To overcome this, the OpenLayers CSS
                    overrides this max-width setting.  If you are 
                    not loading the OpenLayers default CSS or are having trouble 
                    with tile sizing and Bootstrap, add the following to your
                    markup:
                
<style>
    img.olTileImage {
        max-width: none;
    }
</style>