Cómo poner una imagen estática de fondo en WordPress

/* Global */
* { margin: 0; padding: 0; }
body { font-size: 12px; font-family: verdana, arial, georgia; color: #333333; }
#main_container { width: 1015px; margin: 0 auto; }
h1,h2,h3,h4,h5,p { margin: 10px 0; }
.left { float: left; }
.right { float: right; }
.clear { clear: both; }
img { border: none; }
a { color: #666; text-decoration: none; }
a:hover { color:#333; }

/* Header */
#header { padding: 10px 0 30px; }
#menu_container { padding-bottom: 25px; }
#menu_container ul { list-style-type: none; margin-right: 25px; float: left; }
#menu_container ul li { float: left; }
#menu_container ul li a { color: #fff; text-decoration: none; background-color: #000; padding: 6px 5px; margin-right: 5px; -moz-border-radius: 5px; -webkit-border-radius: 5px; -khtml-border-radius: 5px; border-radius: 5px; display: block; }
#menu_container ul li a:hover { background-color: #74ad70; }
#menu_container ul li.current-menu-item a, #menu_container ul li.current_page_item a { background-color: ##74ad70; }
#menu_container input[type=text] { width: 172px; height: 25px; background-color: #000; color: #fff; -moz-border-radius: 5px; -webkit-border-radius: 5px; -khtml-border-radius: 5px; border-radius: 5px; float: right; border: none; padding: 0 5px; }

.header_social_icons_cont { float: right; margin-right: 5px; }
.header_social_icons_cont img { float: left; margin-right: 7px; }

/* Content */
.home_post_cont { float: left; margin-right: 34px; width: 228px; min-height: 331px; margin-bottom: 35px; position: relative; }
.home_post_cont_last { margin-right: 0; }
.home_post_cont img { width: 228px; height: 331px; -moz-border-radius: 5px; -webkit-border-radius: 5px; -khtml-border-radius: 5px; border-radius: 5px; }
.home_post_cont h3 { font-size: 14px; }
.home_post_cont h3 a { color: #000; text-decoration: none; }
.home_post_cont h3 a:hover {  text-decoration: none; color: #666; }

.home_post_content { color: #A0A0A0; font-size: 12px; padding-right: 30px; font-weight: normal; height: 270px; }
.home_post_content .in_title { color: #fff; font-size: 14px; margin: 0; font-weight: bold; }
.home_post_content h4 a { color: #fff; font-size: 14px; margin: 0; }
/*.home_post_cat { position: absolute; bottom: -20px; left: 10px; color: #A0A0A0; font-size: 10px; font-weight: normal; padding-right: 40px; }*/
.home_post_cat { color: #A0A0A0; font-size: 10px; font-weight: normal; padding-right: 40px; }
.home_post_cat a { color: #A0A0A0 !important; text-decoration: none; }
.home_post_cat a:hover {  text-decoration: none; color: #666; }

.single_left { float: left; width: 665px; }
.single_left h1 { font-size: 13px; margin-top: 0; }

    .hover_caption {
      /* If you can count of CSS3 support: */
      background-color: /*rgba(0, 0, 0, 0.7)*/ #000; -moz-border-radius: 5px; -webkit-border-radius: 5px; -khtml-border-radius: 5px; border-radius: 5px;
  
      /* Or use a transparent image if you need to support bad browsers: */
      /*background-image: url(http://www.advientocreativo.com/wp-content/uploads/2013/11/fondo-1024x489.png);*/
  
      /* NOTE: If you're img elements have paddings or margins you'll need to
      match them here to get things lined up properly. */
    }
  
#commentform input[type=submit] { background-color: #000; border: none; color: #fff; padding: 8px 10px; }
#commentform a { color: #000; }

.commentlist a { color: #000; }    
.iphone-home-image { width: 300px !important; }

/* Sidebar */
#sidebar { float: right; width: 270px; }
.side_box { margin-bottom: 25px; }
.side_box h3 { padding: 5px 5px; background-color: #000; margin-top: 0; color: #fff; }
.side_box p { padding: 0px 5px; }
.side_box ul { list-style-type: none; margin-left: 5px; }
.side_box ul li { margin-bottom: 3px; }
.textwidget { padding: 5px; }

/* Footer */
#footer { margin: 25px 0; padding: 12px 0; border-top: 1px solid #CBCBCB; border-bottom: 1px solid #CBCBCB; color: #fff; text-align: center; }
#footer a { color: #fff; text-decoration: none; }
#footer a:hover { text-decoration: underlined; }


#infscr-loading { text-align: center; }


 [MENTION=16931]medi[/MENTION]a screen and (max-width: 480px) {

#main_container { width: 320px; }
#menu_container { display: none; }
.home_post_cont { margin-right: auto; margin-left: auto; float: none; clear: both; }
#footer { display: none; }
#commentform textarea { width: 220px; }
#sidebar { display: none; }
.single_left { float: none; width: 228px; margin-left: auto; margin-right: auto; }
.single_left img { width: 228px; height:inherit; }

}