В начале nav и div классы, в конце закрытие этих классов и перенос строки.
В каждую ссылку добавить клас "nav-link"
<div class="nav-scroller bg-white box-shadow"> <nav class="nav nav-underline">
<a class="nav-link" href="javascript:tag(\'\', \'\')"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/bold.gif" alt="b" title="' . self::$lng['tag_bold'] . '" /></a>
<a class="nav-link" href="javascript:tag(\'\', \'\')"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/italics.gif" alt="i" title="' . self::$lng['tag_italic'] . '" /></a>
<a class="nav-link" href="javascript:tag(\'\', \'\')"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/underline.gif" alt="u" title="' . self::$lng['tag_underline'] . '" /></a>
<a class="nav-link" href="javascript:tag(\'\', \'\')"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/strike.gif" alt="s" title="' . self::$lng['tag_strike'] . '" /></a>
<a class="nav-link" href="javascript:tag(\'\', \'\')"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/list.gif" alt="s" title="' . self::$lng['tag_list'] . '" /></a>
<a class="nav-link" href="javascript:tag(\'[spoiler=]\', \'[/spoiler]\');"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/sp.gif" alt="spoiler" title="Спойлер" /></a>
<a class="nav-link" href="javascript:tag(\'\', \'\')"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/quote.gif" alt="quote" title="' . self::$lng['tag_quote'] . '" /></a>
<a class="nav-link" href="javascript:tag(\'[url=]\', \'[/url]\')"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/link.gif" alt="url" title="' . self::$lng['tag_link'] . '" /></a>
<a class="nav-link" href="javascript:show_hide(\'code\');"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/php.gif" title="Code" alt="Code" /></a>
<a class="nav-link" href="javascript:show_hide(\'color\');"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/color.gif" title="' . self::$lng['color_text'] . '" alt="color" /></a>
<a class="nav-link" href="javascript:show_hide(\'bg\');"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/color_bg.gif" title="' . self::$lng['color_bg'] . '" alt="bg color" /></a>';
if (self::$user_id) {
$out .= ' <a class="nav-link" href="javascript:show_hide(\'sm\');"><img style="border: 0;" src="' . self::$system_set['homeurl'] . '/images/bb/smileys.gif" alt="sm" title="' . self::$lng['smileys'] . '" /></a><br />
<div id="sm" style="display:none">' . $bb_smileys . '</div></nav></div>';
} else {
$out .= '</nav></div><br />';
}