php if else and css position

i try a if else and css position but i cant solve. i need a dynamic position for if empty or not empty.

a1 is not empty top:130; a1 empty > a2 not empty top:130; ++
a2 is not empty top:140; a2 empty > a3 not empty top:140; ++
a3 is not empty top:150; 
a4 is not empty top:160;


a1 a2 a3 is empty > a4 not empty top:130; etc.

i try this

    if ( empty($a1) ) {} else {
$bir = '<div style="position:fixed; float:left; left: 1mm; '.$deger1.' padding: 0.5mm; padding-top: 2mm;">
'.$a1.'
</div>';
};
if ( empty($a2) ) {} else {
$iki = '<div style="position:fixed; float:left; left: 1mm; '.$deger2.' padding: 0.5mm; padding-top: 2mm;">
'.$a2.'
</div>';
};
if ( empty($a3) ) {} else {
$uc = '<div style="position:fixed; float:left; left: 1mm; '.$deger3.' padding: 0.5mm; padding-top: 2mm;">
'.$a3.'
</div>';
};
if ( empty($a4) ) {} else {
$dort = '<div style="position:fixed; float:left; left: 1mm; '.$deger4.' padding: 0.5mm; padding-top: 2mm;">
'.$a4.'
</div>';
};