Final Answer
HTML Document (index.html):
```html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Baking Procedures</title>
<link rel="stylesheet" href="styles.css">
</head>
<body>
<h1>Baking Procedures</h1>
<dl>
<dt><h2>The Ingredients</h2></dt>
<dd>
<ul>
<li>100 g. flour</li>
<li>10 g. sugar</li>
<li>1 cup water</li>
<li>2 eggs</li>
<li>salt, pepper</li>
</ul>
</dd>
<dt><h2>The Procedures</h2></dt>
<dd>
<ol>
<li>1. Mix dry ingredients thoroughly.</li>
<li>2. Pour in wet ingredients.</li>
<li>3. Mix for 10 minutes.</li>
<li>4. Bake for one hour at 300 degrees.</li>
</ol>
</dd>
<dt><h2>Note</h2></dt>
<dd>
<p>The recipe may be improved by adding raisins.</p>
</dd>
</dl>
</body>
</html>
```
**CSS Document (styles.css):**
```css
/* 1. Comments */
/* Style for the body */
/* Adjustments for the header one */
body {
font-family: "Arial", "Helvetica", sans-serif;
}
ol {
font-style: italic;
text-decoration: underline;
}
ul {
font-style: italic;
text-decoration: underline;
margin-left: 20px;
}
h1 {
font-style: italic;
text-decoration: underline;
}
```
Step-by-step explanation
In the HTML document, a structure is created with nested elements to represent the baking procedures. The document includes a definition list (`<dl>`) containing two sets of terms and descriptions, representing the ingredients and procedures, respectively. Each set is formatted with an unordered list (`<ul>`) for ingredients and an ordered list (`<ol>`) for procedures. The "Note" section is a simple paragraph (`<p>`). Additionally, the document follows proper semantic HTML5 structure.
In the CSS document, an external stylesheet (`styles.css`) is linked to the HTML file. The styles include comments for clarity. The body is set to use the "Arial", "Helvetica", and sans-serif fonts.
Ordered and unordered lists are styled with italic and underline, providing a visual distinction. The unordered list under "The Ingredients" is indented by 20 pixels using the `margin-left` property.
Finally, the header one (`<h1>`) is styled with italic and underline, ensuring a consistent look for the main header. The use of an external CSS file promotes maintainability and separation of concerns in web development.