CSS / HTML内联和居中两个单独表单的表单按钮

I am trying to display two form buttons (each belonging to a separate form) inline and centered (Horizontally).
Here's my code:

<div>

<?php
    if(($id && $upperConvLim) || ($id && !$upperConvLim && !$lowerConvLim)){
?>

    <span> &nbsp;&nbsp;&nbsp; </span>
    <form method="post" action="index.php" class="previous">
        <input type="submit" value="Previous" name="submit1" />
        <?php echo '<input type = "hidden" value="'.$id.'"name = "id" />'; ?>
        <?php echo '<input type = "hidden" value="'.$previous.'"name = "previous" />'; ?    >
    </form>

<?php
    }
    if(($id && $lowerConvLim) || ($id && !$upperConvLim && !$lowerConvLim)){
?>

    <span> &nbsp;&nbsp;&nbsp; </span>
    <form method="post" action="index.php" class="next">
        <input type="submit" value="Next" name="submit2" />
        <?php echo '<input type = "hidden" value="'.$id.'"name = "id" />'; ?>
        <?php echo '<input type = "hidden" value="'.$next.'"name = "next" />'; ?>
    </form>

<?php
    }
?>  

</div>

I tried to inline them using the following in my CSS,

form, form div {
    display: inline-block;
}

This works fine but I'm unable to center the two buttons. I would like to know both 1) How to center the two buttons as well as 2) If there is a better way to inline them. Appreciate it.

EDIT: Following Cynthia's suggestion, I changed my php/html code to,

<div class="center-form">
<?php
if(($id && $upperConvLim) || ($id && !$upperConvLim && !$lowerConvLim)){
?>
<span> &nbsp;&nbsp;&nbsp; </span>

<form method="post" action="index.php" class="hform">
        <input type="submit" value="Previous" name="submit1" />
        <?php echo '<input type = "hidden" value="'.$id.'"name = "id" />'; ?>
        <?php echo '<input type = "hidden" value="'.$previous.'"name = "previous" />'; ?>
</form>

<?php
}

if(($id && $lowerConvLim) || ($id && !$upperConvLim && !$lowerConvLim)){
?>

<span> &nbsp;&nbsp;&nbsp; </span>

<form method="post" action="index.php" class="hform">
        <input type="submit" value="Next" name="submit2" />
        <?php echo '<input type = "hidden" value="'.$id.'"name = "id" />'; ?>
        <?php echo '<input type = "hidden" value="'.$next.'"name = "next" />'; ?>
</form>


<?php

}

?>
</div>

And my new CSS:

table {
font-family: Verdana;
font-size: 10pt
}


#table4 {
margin-left: auto;
margin-right: auto;
border:1px solid black;
width :70%;
padding:10px;
background-color:#FAFAD2;
}


#table3 {
margin-left: auto;
margin-right: auto;
border:1px solid black;
width :60%;
padding:10px;
background-color:#FFDAB9;
}

/*
form, form div {

  display: inline-block;
  text-align: center;
}
*/

.center-form { display:block ; width:165px ; margin:auto }

form.hform { display:inline }

input[type=submit] { padding:4px 0 ; width:80px } 

Thanks!

This will centre all all elements within a div or form.

form, form div {
   text-align: center;
}

Here you go: http://jsfiddle.net/myQtb/

In a nutshell:

Here is the abbreviated HTML code (I just used barebones forms):

<div class="center-form">
<form class="hform">
<input type="submit" name="submit" value="Submit">
</form>

<form class="hform">
    <input type="submit" name="submit" value="Reset">
</form>
</div>​

and here is the CSS:

.center-form { display:block ; width:165px ; margin:auto }
form.hform { display:inline }
input[type=submit] { padding:4px 0 ; width:80px }​

Why it works:

Change your form tag styling from inline-block to simply inline. Then enclose BOTH forms in the .center-form DIV that is as wide as the combined width of both buttons. Assign display:block to the .center-form DIV and add margin:auto (so that the left / right margins will auto adjust).

And voila!