Grey plaintext background, header styles

templates/snippets/show.tera

       }
 
       .header {
+        align-items: baseline;
+        display: flex;
+        justify-content: space-between;
         padding: 15px;
       }
 
       }
 
       pre {
+        background-color: #f5f5f5;
         counter-reset: line;
         font-size: 16px;
         padding: 15px;