一共写了9种样式。其中一个是无边框透明的。也凑数放一起了（但也带格式的）。效果可以查看下边的演示页面。
经后续测试发现: 此文章css样式部分效果在安卓Android设备上会出现部分不兼容无法显示完整效果。如天空之境在安卓设备上显示是纯粉色。PC和iOS均显示正常。

效果图：

第一步

首先把下面的CSS丢到你的主题style.css样式文件内。圆角值修改下边的第三行即可。默认8px

/*WordPress宇宙超级无敌美化框 by:zmki  www.zmki.cn/5458.html*/
#wpmel_mhz,#wpmel_xgh,#wpmel_tkzj,#wpmel_xyz,#wpmel_gll ,#wpmel_xty,#wpmel_yyz,#wpmel_szh,#wpmel_wbk{
	/*圆角值,在此定义*/
	border-radius: 8px;
}
/*迷幻紫*/
#wpmel_mhz{
    color: #555555;
    overflow: hidden;
    margin: 10px 0;
    padding: 15px 15px 15px 35px;
    /*border-radius: 10px;*/
    box-shadow: 6px 0 12px -5px rgb(190, 196, 252), -6px 0 12px -5px rgb(189, 196, 252);
    background-color: #8EC5FC;
    background-image: linear-gradient(62deg,#8EC5FC 0%,#E0C3FC 100%);
    background-image: -webkit-linear-gradient(62deg,#8EC5FC 0%,#E0C3FC 100%);
}
/*西瓜红*/
#wpmel_xgh{
	    color: #555555;
    overflow: hidden;
    margin: 10px 0;
    padding: 15px 15px 15px 35px;
    /*border-radius: 10px;*/
    box-shadow: 6px 0 12px -5px rgb(255, 176, 172), -6px 0 12px -5px rgb(255, 161, 174);
    background-color: #ff9a8b66;
    background-image: linear-gradient(220deg,#FF9A8B 0%,#ff6a8838 55%,#FF99AC 100%);
    background-image: -webkit-linear-gradient(220deg,#ff9a8b7a 0%,#ff6a88ab 55%,#ff99ac82 100%);
}
/*华为P30 天空之境*/
#wpmel_tkzj {
    color: #555555;
    overflow: hidden;
    margin: 10px 0;
    padding: 15px 15px 15px 35px;
    /*border-radius: 10px;*/
    box-shadow: 6px 0 12px -5px rgb(253, 223, 234), -6px 0 12px -5px rgb(215, 240, 243);
    background-color: #FFDEE9;
    background-image: linear-gradient(0deg,#ffdee9c4 0%,#b5fffc8f 100%);
    background-image: -webkit-linear-gradient(0deg,#ffdee9c4 0%,#b5fffc8f 100%);
}
/*小宇宙*/
#wpmel_xyz {
    color: #eeeeee;
    overflow: hidden;
    margin: 10px 0;
    padding: 15px 15px 15px 35px;
    /*border-radius: 10px;*/
    box-shadow: 6px 0 12px -5px rgb(12, 85, 141), -6px 0 12px -5px rgba(10, 58, 93, 0);
    background-image: radial-gradient( circle 263px at 100.2% 3%, rgba(12,85,141,1) 31.1%, rgba(205,181,93,1) 36.4%, rgba(244,102,90,1) 50.9%, rgba(199,206,187,1) 60.7%, rgba(249,140,69,1) 72.5%, rgba(12,73,116,1) 72.6% );
}
/*橄榄绿*/
#wpmel_gll {
    color: #eeeeee;
    overflow: hidden;
    margin: 10px 0;
    padding: 15px 15px 15px 35px;
    /*border-radius: 10px;*/
    box-shadow: 6px 0 12px -5px rgb(68, 110, 92), -6px 0 12px -5px rgb(204, 212, 163);
    background-image: linear-gradient( 102deg, rgba(68,110,92,1) 17.4%, rgba(107,156,120,1) 49.3%, rgba(154,183,130,1) 83.4%, rgba(247,237,191,1) 110.3% );
}
/*小太阳*/
#wpmel_xty {
    color: #ffffff;
    overflow: hidden;
    margin: 10px 0;
    padding: 15px 15px 15px 35px;
     /*border-radius: 10px; */
    box-shadow: 6px 0 12px -5px rgb(253, 223, 234), -6px 0 12px -5px rgb(215, 240, 243);
    background-image: radial-gradient( circle farthest-corner at -8.9% 51.2%, rgba(255,124,0,1) 0%, rgba(255,124,0,1) 15.9%, rgba(255,163,77,1) 15.9%, rgba(255,163,77,1) 24.4%, rgba(19,30,37,1) 24.5%, rgba(19,30,37,1) 66% );
}
/*优雅紫*/
#wpmel_yyz {
	color: #ffffff;
    overflow: hidden;
    margin: 10px 0;
    padding: 15px 15px 15px 35px;
    /*border-radius: 10px;*/
    box-shadow: 6px 0 12px -5px rgb(175, 160, 208), -6px 0 12px -5px rgba(177, 161, 207, 0);
    background-image: radial-gradient( circle farthest-corner at 10% 20%, rgba(95,117,227,1) 0%, rgba(188,167,205,1) 90% );
}
/*深邃黑*/
#wpmel_szh {
	color: #c7c7c7;
    overflow: hidden;
    margin: 10px 0;
    padding: 15px 15px 15px 35px;
    /*border-radius: 5px;*/
    box-shadow: 6px 0 12px -5px rgb(155, 170, 185), -6px 0 12px -5px rgba(177, 161, 207, 0);
    background-image: radial-gradient( circle farthest-corner at 10% 20%, rgba(0,0,0,1) 0%, rgba(64,64,64,1) 90.2% );
}
/*无边框*/
#wpmel_wbk {
    color: #000000;
    overflow: hidden;
    margin: 10px 0;
    padding: 15px 15px 15px 35px;
}
#wpmel_xyz a , #wpmel_gll a{
	 color: #eeeeee;
}
#wpmel_szh a{
	color: #c7c7c7;	
}
#wpmel_xty a, #wpmel_yyz a{
	color: #ffffff;
}

第二步

然后把下面的代码放到你主题的函数文件functions.php内

 add_action('after_wp_tiny_mce', 'bolo_after_wp_tiny_mce');
 function bolo_after_wp_tiny_mce($mce_settings) {
 ?>
 <script type="text/javascript"> 
 QTags.addButton( 'z_mhz', '迷幻紫', '<div id="wpmel_mhz">迷幻紫</div>\n', "" );
 QTags.addButton( 'z_xgh', '西瓜红', '<div id="wpmel_xgh">西瓜红</div>\n', "" );
 QTags.addButton( 'z_tkzj', '天空之境', '<div id="wpmel_tkzj">天空之境</div>\n', "" );
 QTags.addButton( 'z_xyz', '小宇宙', '<div id="wpmel_xyz">小宇宙</div>\n', "" );
 QTags.addButton( 'z_gll', '橄榄绿', '<div id="wpmel_gll">橄榄绿</div>\n', "" );
 QTags.addButton( 'z_xty', '小太阳', '<div id="wpmel_xty">小太阳</div>\n', "" );
 QTags.addButton( 'z_yyz', '优雅紫', '<div id="wpmel_yyz">优雅紫</div>\n', "" );
 QTags.addButton( 'z_szh', '深邃黑', '<div id="wpmel_szh">深邃黑</div>\n', "" );
 QTags.addButton( 'z_wbk', '无边框', '<div id="wpmel_wbk">无边框</div>\n', "" ); 
 function bolo_QTnextpage_arg1() {
 }
 </script>
 <?php
 }

如何使用？

如图，WordPress后台文章编辑器 文本选项插入相应文本框即可。可返回可视化编辑操作。如换行不生效可检查div嵌套关系。