IDs must be unique to an HTML document.
If a class name you have selected is very similar to an HTML element name, this often indicates that your HTML can be more semantic. Use <footer>I am a footer</footer> instead of <div class=”footer”>I am a footer</div>.
Code such as <h1 class=”largeHeading”>Title</h1> is redundant since h1 means “largeHeading.” A preferable class name would be more specific and indicate how the heading is used. For example, <h1 class=”masthead”>Title</h1>, would indicate both how and where the class is used.
Missing the alt attribute for an image may seem like a small thing, but it is important for accessibility and it is required.