trying to user left margin 50px on this link but it no working. 
index.php
echo "<a href=\"zoom.php?img={$row['image_id']}\"> <b id='bold2'>" . $image_short_name_db . "</b></a>";


c.css
.bold2
{
    margin-left:50px;
}

Thats because a . in CSS refers to a class, not an id.

/** Id syntax */
#bold2 {margin-left:50px;}

/** Class syntax */
.bold2 {margin-left:50px;}
commented: thanks +2