А не проще взять стиль Mybb Romantic NewYear и не много его подработать?

<style>
HTML, BODY {background-image: url(http://s45.radikal.ru/i110/1001/d4/73d7f099b5f1.jpg); background-repeat: repeat-x; background-attachment: fixed; background-position: top center;}
.punbb .section .container, .punbb .post-body, .punbb .post-links, .punbb td.tc2, .punbb td.tc3,
.punbb .formal fieldset .post-box, #viewprofile li strong, #viewprofile li div, #setmods dd,
.punbb .info-box, .punbb #pun-main .info-box .legend, .punbb .main .container, .punbb .post .container, .punbb .post h3, #pun-stats h2, .punbb .main h1, .punbb .main h2, #pun-title, #pun-title .container, .punbb .modmenu .container, .punbb legend span, #viewprofile h2 span, #profilenav h2 span, .punbb .post h3 span, .punbb th, #viewprofile li, #setmods dl, .punbb .quote-box, .punbb .code-box, #pun-navlinks .container, #pun{
background: none #000 !important;
color: #fff;
}

*{
border: none !important;
}
</style>