Bootstrap 3 or 4

//Content
echo "<div class='container-flex'>n";
 echo "<div class='row'>n";
 echo "<div class='col-xs-12 col-sm-12 col-md-12 col-lg-12'>".AU_CENTER."</div>n";
 echo "</div>n";

 if (LEFT) {
 echo "<div class='row'>n";
 echo "<div class='col-xs-2 col-sm-2 col-md-2 col-lg-2'>".LEFT."</div>n";
 }
 echo "<div class='col-xs-8 col-sm-8 col-md-8 col-lg-8'>".U_CENTER.CONTENT.L_CENTER."</div>";
 if (RIGHT) {
 echo "<div class='col-xs-2 col-sm-2 col-md-2 col-lg-2'>".RIGHT."</div>n";
 }
 echo "</div>n";
 echo "<div class='row'>n";
 echo "<div class='col-xs-12 col-sm-12 col-md-12 col-lg-12'>".BL_CENTER."</div>n";
 echo "</div>n";
echo "</div>n";

echo AU_CENTER ? "<div class='au-content'>".AU_CENTER."</div>n" : '';
echo "<div class='row'>n";
echo "<div class='col-xs-12 col-sm-2 col-md-2 col-lg-2 leftbar'>n";
echo LEFT.RIGHT;
echo "</div>n";
echo "<div class='col-xs-12 col-sm-10 col-md-10 col-lg-10 main-content'>n";
echo U_CENTER.CONTENT.L_CENTER;
echo "</div>n";
//echo "<div class='col-xs-12 col-sm-2 col-md-2 col-lg-2 rightbar'>n";
//echo RIGHT;
//echo "</div>n";
echo BL_CENTER ? "<div class='bl-content'>".BL_CENTER."</div>n" : '';
echo "</div>n";