docs: Fix usage of passing info to a div and not the body (#5577)

# Description
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**Type of change**
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- Documentation update

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- I added relevant documentation

argilla/docs/how_to_guides/custom_fields.md

@@ -178,8 +178,18 @@ When `advanced_mode=True`, you can use the `template` argument to pass a full HT
 Let's reproduce example from the [Without advanced mode](#without-advanced-mode) section but this time we will insert the [handlebars syntax engine](https://handlebarsjs.com/) into the template ourselves.
 
 ```python
-render_template = """
+template = """
+<div id="content"></div>
 <script id="template" type="text/x-handlebars-template">
+    <style>
+    #container {
+        display: flex;
+        gap: 10px;
+    }
+    .column {
+        flex: 1;
+    }
+    </style>
     <div id="container">
         <div class="column">
             <h3>Original</h3>
@@ -199,13 +209,13 @@ script = """
     const template = document.getElementById("template").innerHTML;
     const compiledTemplate = Handlebars.compile(template);
     const html = compiledTemplate({ record });
-    document.body.innerHTML = html;
+    document.getElementById("content").innerHTML = html;
 </script>
 """ # (2)
 ```
 
-1. This is a JavaScript template script. We set `id` to `template` to use it later in our JavaScript code and `type` to `text/x-handlebars-template` to indicate that this is a Handlebars template.
-2. This is a JavaScript template script. We load the Handlebars library and then use it to compile the template and render the record.
+1. This is a JavaScript template script. We set `id` to `template` to use it later in our JavaScript code and `type` to `text/x-handlebars-template` to indicate that this is a Handlebars template. Note that we also added a `div` with `id` to `content` to render the template into.
+2. This is a JavaScript template script. We load the Handlebars library and then use it to compile the template and render the record. Eventually, we render the result into the `div` with `id` to `content`.
 
 We can now pass these templates to the `CustomField` class, ensuring that the `advanced_mode` is set to `True`.
 
@@ -214,7 +224,7 @@ import argilla as rg
 
 custom_field = rg.CustomField(
     name="image",
-    template=render_template + script,
+    template=template + script,
     advanced_mode=True
 )
 ```