Internal style does not work in this HTML code?

<html>
<head>
<style>
#1fineday {
    color:yellow;
}
</style>
</head>
<body>
<h1>Welcome</h1>
<div class="intro">
  <p id="1fineday">Hello World</p> 
</div>
</body>
</html>

Shouldn't "Hello World" be yellow? I don't understand why internal CSS styling I wrote doesn't apply. The ID is 1fineday. I must be overlooking something.

Solution

Because of naming convention, your id cannot start with a number

<html>

<head>
  <style>
    #fineday {
      color: yellow;
    }
  </style>
</head>

<body>
  <h1>Welcome</h1>
  <div class="intro">
    <p id="fineday">Hello World</p>
  </div>
</body>

</html>

Remove the number 1 and it will work

For reference:

W3Schools: https://www.w3schools.com/css/css_syntax.asp

CSS-Tricks: https://css-tricks.com/ids-cannot-start-with-a-number/