Q:

How to place an element to be glued at the right of a div?

There is a fieldset that I want to place just after a div; here is what I have attempted:
<div id="liste_tables">
    <div id="salles"> // div I want the fieldset to be close to
        <div class="header">Salle</div>
        <div class="flex-grid">
            <?php
            $salles = Salle::lireParCritere([]);
            foreach ($salles as $key => $salle) {
            ?>
            <div class="row">
                <div class="cell">
                    <div id="tile_salle_<?php echo $key; ?>" data-pk="<?php echo $salle->salle_code; ?>" class="tile-square fg-white">
                        <div class="tile-content">
                            <div class="image-container">
                                <div class="frame"><img src="<?php echo HTTP_IMG ?>salle.jpg"/></div>
                                <div class="tile-label header fg-cyan"><?php echo $salle->salle_lib; ?></div>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
            <?php } ?>
        </div>
    </div>
    <fieldset>
        <legend class="header">Tables</legend>
        <div id="tables"></div>
    </fieldset> 
</div>

At runtime the fieldset is at the bottom of the div. So how to place the fieldset just after the div with the ID "#salles" ?
EDIT : You can find the css here ; the concerned css is metro.css.
Here is the JsFiddle.

A:

Ok , I found it ; I changed the container to be a MetroUI condensed grid :
<div id="liste_tables" class="grid condensed">
    <div class="row cells4">
        <div class="cell"><span class="header">Salle</span></div>
        <div class="cell colspan3"><span class="header">Tables</span></div>
    </div>
    <div class="row cells4">
        <div class="cell">
            <div class="grid condensed">
                <?php
                $salles = Salle::lireParCritere([]);
                foreach ($salles as $key => $salle) {
                ?>
                <div class="row">
                    <div class="cell">
                        <div id="tile_salle_<?php echo $key; ?>" data-pk="<?php echo $salle->salle_code; ?>" class="tile-square fg-white">
                            <div class="tile-content">
                                <div class="image-container">
                                    <div class="frame"><img src="<?php echo HTTP_IMG ?>salle.jpg"/></div>
                                    <div class="tile-label header fg-cyan"><?php echo $salle->salle_lib; ?></div>
                                </div>
                            </div>
                        </div>
                    </div>
                </div>
                <?php } ?>
            </div>
        </div>
        <div class="cell colspan3">
            <div id="tables"></div>
        </div>
    </div>
</div>

