I looked into your code. You have:
- '<DOCUTYPE! HTML>' instead of '<DOCTYPE! html>'
- you have only one 'h1' on your page, so you don't need 'id="title"' for it. You can just use 'h1' (or 'header h1' or 'header > h1') in your CSS
- 'h1' should be clickable and follow to main page, link 'home' in navigation is unnecessary
- again: you have only one 'nav' with 'ul', so you don't need 'id="nav_links"' for 'ul'.
- 'id="section_heading"' for more than one element
- unnecessary 'class="paragraphs"' for 'p', you can use 'section p' in your CSS
- instead of '<div id="footer">' you can use new tag 'footer' from html5
- '</div' without '>' before '</body>'