Centre a doubleclick ad - html

Question

I'm not sure how to centre a doubleclick ad horizontally. After reading this similar question Centre align leaderboard ad, I'm using this code now
<div class="center">
<style type="text/css">
.center {
text-align: center;
margin: 0 auto;
}
</style>
AD CODE
</div>
But it doesn't work. Any ideas?
To clarify, the ad is being used on this website. http://worldgreendaily.com/
The total code on the page is:
<?php
if ( ! defined( 'ABSPATH' ) ) exit; // Exit if accessed directly
$page_layout = get_option(THEME_NAME."_page_layout");
//logo settings
$logo = get_option(THEME_NAME.'_logo');
$search = get_option(THEME_NAME.'_search');
//top banner
$topBanner = get_option(THEME_NAME."_top_banner");
$topBannerCode = get_option(THEME_NAME."_top_banner_code");
//fixed menu
$menuStyle = get_option(THEME_NAME."_menu_style");
$weatherSet = get_option(THEME_NAME."_weather");
$weather = OT_weather_forecast($_SERVER['REMOTE_ADDR']);
// header social icons
$socialHeader = get_option(THEME_NAME."_social_header");
$vimeo = get_option(THEME_NAME."_vimeo");
$twitter = get_option(THEME_NAME."_twitter");
$facebook = get_option(THEME_NAME."_facebook");
$googlepluss = get_option(THEME_NAME."_googlepluss");
$pinterest = get_option(THEME_NAME."_pinterest");
$tumblr = get_option(THEME_NAME."_tumblr");
$linkedin = get_option(THEME_NAME."_linkedin");
$dribbble = get_option(THEME_NAME."_dribbble");
$soundcloud = get_option(THEME_NAME."_soundcloud");
?>
<!-- BEGIN .boxed -->
<div class="boxed<?php echo $page_layout=="boxed" ? " active" : false; ?>">
<!-- BEGIN .header -->
<div class="header">
<!-- BEGIN .header-very-top -->
<div class="header-very-top">
<!-- BEGIN .wrapper -->
<div class="wrapper">
<div class="left">
<?php
if ( function_exists( 'register_nav_menus' )) {
$walker = new OT_Walker_Top;
$args = array(
'container' => '',
'theme_location' => 'top-menu',
'items_wrap' => '<ul class="ot-menu very-top-menu load-responsive" rel="'.__("Top Menu", THEME_NAME).'"><li><i class="fa fa-home"></i></li>%3$s</ul>',
'depth' => 3,
'walker' => $walker,
"echo" => false
);
if(has_nav_menu('top-menu')) {
echo wp_nav_menu($args);
}
}
?>
</div>
<?php if($weatherSet=="on") { ?>
<?php if(!isset($weather['error'])) { ?>
<div class="right">
<div class="weather-report">
<span><?php _e("Weather",THEME_NAME);?></span>
<b><?php echo $weather['country'].', '.$weather['city'];?></b>
<img src="<?php echo THEME_IMAGE_URL.$weather['image'];?>.png" alt="<?php echo $weather['country'].', '.$weather['city'];?>" />
<font class="weather-meter" style="background: <?php echo $weather['color'];?>;"><?php echo $weather['temp_'.get_option(THEME_NAME."_temperature")];?></font>
</div>
</div>
<?php
} else {
echo $weather['error'];
}
?>
<?php } ?>
<div class="clear-float"></div>
</div>
<div class="double-split"></div>
<!-- END .header-very-top -->
</div>
<!-- BEGIN .header-middle -->
<div class="header-middle">
<div class="wrapper">
<?php if($logo) { ?>
<div class="logo-image">
<h1><?php bloginfo('name'); ?></h1>
<img class="logo" src="<?php echo $logo;?>" alt="<?php bloginfo('name'); ?>" />
</div>
<?php } else { ?>
<div class="logo-text">
<h1><?php bloginfo('name'); ?></h1>
</div>
<?php } ?>
<?php if($topBanner=="on") { ?>
<div class="banner">
<div class="banner-block">
<?php echo stripslashes(do_shortcode($topBannerCode));?>
</div>
<?php if (is_pagetemplate_active("template-contact.php")) { ?>
<?php $contactID = ot_get_page('contact'); ?>
<div class="banner-info">
<span class="icon-default"> </span><?php _e("Sponsored Advert", THEME_NAME);?><span class="icon-default"> </span>
</div>
<?php } ?>
</div>
<?php } ?>
<div class="clear-float"></div>
</div>
<!-- END .header-middle -->
</div>
<!-- BEGIN .header-menu -->
<div class="header-menu<?php if($menuStyle=='on') { echo ' thisisfixed'; } ?>">
<div class="wrapper">
<?php
wp_reset_query();
if ( function_exists( 'register_nav_menus' )) {
$walker = new OT_Walker;
$args = array(
'container' => '',
'theme_location' => 'middle-menu',
'items_wrap' => '<ul class="%2$s main-menu" >%3$s</ul>',
'depth' => 3,
"echo" => false,
'walker' => $walker
);
if(has_nav_menu('middle-menu')) {
echo wp_nav_menu($args);
} else {
echo "<ul class=\"main-menu\"><li class=\"navi-none\">Please set up ".THEME_FULL_NAME." menu!</li></ul>";
}
}
?>
<?php if($search=="on") { ?>
<div class="right menu-search">
<form method="get" action="<?php echo home_url(); ?>" name="searchform" >
<input type="text" value="" placeholder="<?php _e("Search something..",THEME_NAME);?>" name="s" id="s"/>
<input type="submit" class="search-button" value=" " />
</form>
</div>
<?php } ?>
<div class="clear-float"></div>
</div>
<!-- END .header-menu -->
</div>
<!-- BEGIN .header-undermenu -->
<div class="header-undermenu">
<div class="wrapper">
<?php
if ( function_exists( 'register_nav_menus' )) {
$args = array(
'container' => '',
'theme_location' => 'third-menu',
"link_before" => '<i>',
"link_after" => '</i>' ,
'items_wrap' => '<ul class="secondary-menu" >%3$s</ul>',
'depth' => 1,
"echo" => false
);
if(has_nav_menu('third-menu')) {
echo wp_nav_menu($args);
}
}
?>
<div class="clear-float"></div>
</div>
<!-- END .header-undermenu -->
</div>
<!-- END .header -->
</div>
<?php wp_reset_query(); ?>
<div style="text-align: center; margin: 0 auto;"><!-- Test_WGD -->
<div id='div-gpt-ad-1419519536676-0' style='width:728px; height:90px;'>
<script type='text/javascript'>
googletag.cmd.push(function() { googletag.display('div-gpt-ad-1419519536676-0'); });
</script></div>
</html>

Answer 1

If you put your css on the page instead of linking to an external css file you should be putting it inside the <head></head> tags. Your document should look something like this:
<html>
<head>
<style type="text/css">
.center {
text-align: center;
margin: 0 auto;
}
</style>
</head>
<body>
<div class="center">AD CODE</div>
</body>
</html>
you can also use inline styling (which I would not recommend) if you wanted the styles near the div like your example:
<div style="text-align: center; margin: 0 auto;">AD CODE</div>
UPDATE
This is being pulled in from an iframe. What you need to do is find the id that I have pointed out in the below image:
Which is this:
<div id='div-gpt-ad-1419519536676-0' style='width:728px; height:90px;'>
and add margin: auto to it, like so:
<div id='div-gpt-ad-1419519536676-0' style='width:728px; height:90px; margin: auto;'>
That should center your image

Answer 2

div and style tags must be replaced.
<html>
<head>
<style type="text/css">
.center {
text-align: center;
margin: 0 auto;
}
</style>
</head>
<body>
<div class="center">
AD CODE
</div>
</body>
</html>