Styling

In HTML, the following style guide and naming conventions should be used for ID’s:

HTML Value Quotation Marks - You should surround your ID value using double quotation marks (as opposed to single).
ID Naming - Use meaningful ID names that reflect the purpose of the element in question, like “contact” rather than “paragraph4”.
Acceptable Characters - Technically, in HTML5, ID names must contain at least one character and no spaces. Which leaves all UTF-8 characters as options. (i.e. a-z, A-Z, 0-9, “_”, “-”, “:;,?!@#$%^&*+”, etc.).

However, due to issues that can arise in element selection with CSS and JavaScript, you should follow a more restrictive naming conventions. These conventions are also intended to lend consistency to code between pages and developers, as well as increase readability.
1. Use lowercase letters or number (i.e. a-z and 0-9).
2. Start an ID name with a lowercase letter.
3. Use hyphens (“-”) to separate words (as opposed to underscores “_” or camelCase).

HTML

<!-- Recommended: -->
<div id="use-double-quotations">
<div id="contact">
<div id="image-gallery-1">

<!-- Bad Style: -->
<div id='do-not-use-single-quotations'>
<div id='paragraph4'>
<div id='Image_Gallery-1!'>

NOTE: You should use ID names that are as short as possible, but as long as necessary. The goal is to clearly convey what the element is without being unnecessarily verbose.