메인 최근갤러리에 배경이미지 넣고싶습니다

<?php
if (!defined('_GNUBOARD_')) exit; // 개별 페이지 접근 불가
include_once(G5_LIB_PATH.'/thumbnail.lib.php');

// add_stylesheet('css 구문', 출력순서); 숫자가 작을 수록 먼저 출력됨
add_stylesheet('<link rel="stylesheet" href="'.$latest_skin_url.'/style.css">', 0);
$thumb_width = 210;
$thumb_height = 150;
$list_count = (is_array($list) && $list) ? count($list) : 0;
?>

<div class="pic_lt">
    <ul>
    <?php
    for ($i=0; $i<$list_count; $i++) {
    $thumb = get_list_thumbnail($bo_table, $list[$i]['wr_id'], $thumb_width, $thumb_height, false, true);

    if($thumb['src']) {
        $img = $thumb['src'];
    } else {
        $img = G5_IMG_URL.'/no_img.png';
        $thumb['alt'] = '이미지가 없습니다.';
    }
    $img_content = '<img src="'.$img.'" alt="'.$thumb['alt'].'" >';
    $wr_href = get_pretty_url($bo_table, $list[$i]['wr_id']);
    ?>
        <li class="galley_li">
            <a href="<?php echo $wr_href; ?>" class="lt_img"><?php echo run_replace('thumb_image_tag', $img_content, $thumb); ?></a>
            <?php
            if ($list[$i]['icon_secret']) echo "<i class=\"fa fa-lock\" aria-hidden=\"true\"></i><span class=\"sound_only\">비밀글</span> ";

            echo "<a href=\"".$wr_href."\"> ";
            if ($list[$i]['is_notice'])
                echo "<strong>".$list[$i]['subject']."</strong>";
            else
                echo $list[$i]['subject'];
            echo "</a>";
            
            if ($list[$i]['icon_new']) echo "<span class=\"new_icon\">N<span class=\"sound_only\">새글</span></span>";
            if ($list[$i]['icon_hot']) echo "<span class=\"hot_icon\">H<span class=\"sound_only\">인기글</span></span>";

            // if ($list[$i]['link']['count']) { echo "[{$list[$i]['link']['count']}]"; }
            // if ($list[$i]['file']['count']) { echo "<{$list[$i]['file']['count']}>"; }

            // echo $list[$i]['icon_reply']." ";
            // if ($list[$i]['icon_file']) echo " <i class=\"fa fa-download\" aria-hidden=\"true\"></i>" ;
            // if ($list[$i]['icon_link']) echo " <i class=\"fa fa-link\" aria-hidden=\"true\"></i>" ;

            if ($list[$i]['comment_cnt'])  echo "
            <span class=\"lt_cmt\">".$list[$i]['wr_comment']."</span>";

            ?>

            <div class="lt_info">
                <span class="lt_nick"><?php echo $list[$i]['name'] ?></span>
                <span class="lt_date"><?php echo $list[$i]['datetime2'] ?></span>              
            </div>
        </li>
    <?php }  ?>
    <?php if ($list_count == 0) { //게시물이 없을 때  ?>
    <li class="empty_li">게시물이 없습니다.</li>
    <?php }  ?>
    </ul>
    <a href="<?php echo get_pretty_url($bo_table); ?>" class="lt_more"><span class="sound_only"><?php echo $bo_subject ?></span>더보기</a>

</div>

@charset "utf-8";

/* 새글 스킨 (latest) */
.pic_lt {position:relative;margin-bottom:20px}
.pic_lt .lat_title {display:block;line-height:45px;font-size:1.2em;color:#253dbe}
.pic_lt .lat_title a {color:#000;display:inline-block;position:relative}

.pic_lt .lt_more {position:absolute;top:11px;right:10px;display:block;width:25px;line-height:25px;color:#aaa;border-radius:3px;text-align:center;}
.pic_lt .lt_more:hover {color:#777}
.pic_lt ul:after {display:block;visibility:hidden;clear:both;content:""}
.pic_lt ul {margin: 0 -10px}
.pic_lt li {float:left;width:173px;padding:0 10px}
.pic_lt li.galley_li:nth-child(4n+1) {clear: both!important}
.pic_lt li .lt_img {margin:5px 0;display:block}
.pic_lt li .lt_img img, .pic_lt li .lt_img video{width:100%;height:auto}
.pic_lt li a:hover {color:#a22121}
.pic_lt li .fa-heart {color:#ff0000}
.pic_lt li .fa-lock {display:inline-block;line-height:14px;width:16px;font-size:0.833em;color:#4f818c;background:#cbe3e8;text-align:center;border-radius:2px;font-size:12px;border:1px solid #cbe3e8;vertical-align:middle}
.pic_lt li .new_icon {display:inline-block;width:16px;line-height:16px;font-size:0.833em;color:#23db79;background:#b9ffda;text-align:center;border-radius:2px;margin-left:2px;font-weight:bold;vertical-align:middle}
.pic_lt li .hot_icon {display:inline-block;width:16px;line-height:16px;font-size:0.833em;color:#ff0000;background:#ffb9b9;text-align:center;border-radius:2px;vertical-align:middle}
.pic_lt li .fa-caret-right {color:#bbb}
.pic_lt li .fa-download {display:inline-block;width:16px;line-height:16px;font-size:0.833em;color:#daae37;background:#ffefb9;text-align:center;border-radius:2px;vertical-align:middle}
.pic_lt li .fa-link {display:inline-block;width:16px;line-height:16px;font-size:0.833em;color:#b451fd;background:#edd3fd;text-align:center;border-radius:2px;vertical-align:middle}

.pic_lt .profile_img img{border-radius:50%}

.lt_info {padding:10px 0}
.lt_info .lt_nick {}
.lt_info .lt_date {color:#888}

.pic_lt .empty_li {line-height:145px ;color:#666;text-align:center;padding:0}
.pic_lt .empty_li:before {background:none;padding:0}

.pic_lt .lt_cmt {background:#e9eff5;color:#3a8afd;font-size:11px;height:16px;line-height:16px;padding:0 5px;border-radius:3px;vertical-align:middle}
.pic_lt .lt_more {position:absolute;top:11px;right:0;display:block;width:40px;line-height:25px;color:#3a8afd;border-radius:3px;text-align:center}
.pic_lt .lt_more:hover {color:#777}