main.css

.container {
  /*
    If you have a block-level element of a certain width, margin: 0 auto;
    will how you center it inside its parent container.

    See: http://bluerobot.com/web/css/center1.html
    
    Don't change the container width.
  */
  margin: 0 auto;  
  width: 720px;
}

ul {
  display: inline-block;
  list-style-type: none;
  padding-left: 0;

}
ul li {
  float: left;
  padding: 10px 0px 10px 0;
  width: 140px;
  text-align: center;
  border-top: 1px solid lightgray;
  border-bottom: 1px solid lightgray;
  border-left: 1px solid lightgray;
  border-right: 1px solid white;
  background: #eeeeee; /* Old browsers */
  background: -moz-linear-gradient(top, #eeeeee 0%, #cccccc 100%); /* FF3.6+ */
  background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,#eeeeee), color-stop(100%,#cccccc)); /* Chrome,Safari4+ */
  background: -webkit-linear-gradient(top, #eeeeee 0%,#cccccc 100%); /* Chrome10+,Safari5.1+ */
  background: -o-linear-gradient(top, #eeeeee 0%,#cccccc 100%); /* Opera 11.10+ */
  background: -ms-linear-gradient(top, #eeeeee 0%,#cccccc 100%); /* IE10+ */
  background: linear-gradient(to bottom, #eeeeee 0%,#cccccc 100%); /* W3C */
  filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#eeeeee', endColorstr='#cccccc',GradientType=0 ); /* IE6-9 */
}

a {
  text-decoration: none;
  color: black;
}

li:first-child {
  border-radius: 10px 0px 0px 10px;
}
li:last-child {
  border-radius: 0px 10px 10px 0px;
  border-right: 1px solid lightgray;
}

normalize.css

/*! normalize.css v2.1.0 | MIT License | git.io/normalize */

/* ==========================================================================
   HTML5 display definitions
   ========================================================================== */

/**
 * Correct `block` display not defined in IE 8/9.
 */

article,
aside,
details,
figcaption,
figure,
footer,
header,
hgroup,
main,
nav,
section,
summary {
    display: block;
}

/**
 * Correct `inline-block` display not defined in IE 8/9.
 */

audio,
canvas,
video {
    display: inline-block;
}

/**
 * Prevent modern browsers from displaying `audio` without controls.
 * Remove excess height in iOS 5 devices.
 */

audio:not([controls]) {
    display: none;
    height: 0;
}

/**
 * Address styling not present in IE 8/9.
 */

[hidden] {
    display: none;
}

/* ==========================================================================
   Base
   ========================================================================== */

/**
 * 1. Set default font family to sans-serif.
 * 2. Prevent iOS text size adjust after orientation change, without disabling
 *    user zoom.
 */

html {
    font-family: sans-serif; /* 1 */
    -webkit-text-size-adjust: 100%; /* 2 */
    -ms-text-size-adjust: 100%; /* 2 */
}

/**
 * Remove default margin.
 */

body {
    margin: 0;
}

/* ==========================================================================
   Links
   ========================================================================== */

/**
 * Address `outline` inconsistency between Chrome and other browsers.
 */

a:focus {
    outline: thin dotted;
}

/**
 * Improve readability when focused and also mouse hovered in all browsers.
 */

a:active,
a:hover {
    outline: 0;
}

/* ==========================================================================
   Typography
   ========================================================================== */

/**
 * Address variable `h1` font-size and margin within `section` and `article`
 * contexts in Firefox 4+, Safari 5, and Chrome.
 */

h1 {
    font-size: 2em;
    margin: 0.67em 0;
}

/**
 * Address styling not present in IE 8/9, Safari 5, and Chrome.
 */

abbr[title] {
    border-bottom: 1px dotted;
}

/**
 * Address style set to `bolder` in Firefox 4+, Safari 5, and Chrome.
 */

b,
strong {
    font-weight: bold;
}

/**
 * Address styling not present in Safari 5 and Chrome.
 */

dfn {
    font-style: italic;
}

/**
 * Address differences between Firefox and other browsers.
 */

hr {
    -moz-box-sizing: content-box;
    box-sizing: content-box;
    height: 0;
}

/**
 * Address styling not present in IE 8/9.
 */

mark {
    background: #ff0;
    color: #000;
}

/**
 * Correct font family set oddly in Safari 5 and Chrome.
 */

code,
kbd,
pre,
samp {
    font-family: monospace, serif;
    font-size: 1em;
}

/**
 * Improve readability of pre-formatted text in all browsers.
 */

pre {
    white-space: pre-wrap;
}

/**
 * Set consistent quote types.
 */

q {
    quotes: "\201C" "\201D" "\2018" "\2019";
}

/**
 * Address inconsistent and variable font size in all browsers.
 */

small {
    font-size: 80%;
}

/**
 * Prevent `sub` and `sup` affecting `line-height` in all browsers.
 */

sub,
sup {
    font-size: 75%;
    line-height: 0;
    position: relative;
    vertical-align: baseline;
}

sup {
    top: -0.5em;
}

sub {
    bottom: -0.25em;
}

/* ==========================================================================
   Embedded content
   ========================================================================== */

/**
 * Remove border when inside `a` element in IE 8/9.
 */

img {
    border: 0;
}

/**
 * Correct overflow displayed oddly in IE 9.
 */

svg:not(:root) {
    overflow: hidden;
}

/* ==========================================================================
   Figures
   ========================================================================== */

/**
 * Address margin not present in IE 8/9 and Safari 5.
 */

figure {
    margin: 0;
}

/* ==========================================================================
   Forms
   ========================================================================== */

/**
 * Define consistent border, margin, and padding.
 */

fieldset {
    border: 1px solid #c0c0c0;
    margin: 0 2px;
    padding: 0.35em 0.625em 0.75em;
}

/**
 * 1. Correct `color` not being inherited in IE 8/9.
 * 2. Remove padding so people aren't caught out if they zero out fieldsets.
 */

legend {
    border: 0; /* 1 */
    padding: 0; /* 2 */
}

/**
 * 1. Correct font family not being inherited in all browsers.
 * 2. Correct font size not being inherited in all browsers.
 * 3. Address margins set differently in Firefox 4+, Safari 5, and Chrome.
 */

button,
input,
select,
textarea {
    font-family: inherit; /* 1 */
    font-size: 100%; /* 2 */
    margin: 0; /* 3 */
}

/**
 * Address Firefox 4+ setting `line-height` on `input` using `!important` in
 * the UA stylesheet.
 */

button,
input {
    line-height: normal;
}

/**
 * Address inconsistent `text-transform` inheritance for `button` and `select`.
 * All other form control elements do not inherit `text-transform` values.
 * Correct `button` style inheritance in Chrome, Safari 5+, and IE 8+.
 * Correct `select` style inheritance in Firefox 4+ and Opera.
 */

button,
select {
    text-transform: none;
}

/**
 * 1. Avoid the WebKit bug in Android 4.0.* where (2) destroys native `audio`
 *    and `video` controls.
 * 2. Correct inability to style clickable `input` types in iOS.
 * 3. Improve usability and consistency of cursor style between image-type
 *    `input` and others.
 */

button,
html input[type="button"], /* 1 */
input[type="reset"],
input[type="submit"] {
    -webkit-appearance: button; /* 2 */
    cursor: pointer; /* 3 */
}

/**
 * Re-set default cursor for disabled elements.
 */

button[disabled],
html input[disabled] {
    cursor: default;
}

/**
 * 1. Address box sizing set to `content-box` in IE 8/9.
 * 2. Remove excess padding in IE 8/9.
 */

input[type="checkbox"],
input[type="radio"] {
    box-sizing: border-box; /* 1 */
    padding: 0; /* 2 */
}

/**
 * 1. Address `appearance` set to `searchfield` in Safari 5 and Chrome.
 * 2. Address `box-sizing` set to `border-box` in Safari 5 and Chrome
 *    (include `-moz` to future-proof).
 */

input[type="search"] {
    -webkit-appearance: textfield; /* 1 */
    -moz-box-sizing: content-box;
    -webkit-box-sizing: content-box; /* 2 */
    box-sizing: content-box;
}

/**
 * Remove inner padding and search cancel button in Safari 5 and Chrome
 * on OS X.
 */

input[type="search"]::-webkit-search-cancel-button,
input[type="search"]::-webkit-search-decoration {
    -webkit-appearance: none;
}

/**
 * Remove inner padding and border in Firefox 4+.
 */

button::-moz-focus-inner,
input::-moz-focus-inner {
    border: 0;
    padding: 0;
}

/**
 * 1. Remove default vertical scrollbar in IE 8/9.
 * 2. Improve readability and alignment in all browsers.
 */

textarea {
    overflow: auto; /* 1 */
    vertical-align: top; /* 2 */
}

/* ==========================================================================
   Tables
   ========================================================================== */

/**
 * Remove most spacing between table cells.
 */

table {
    border-collapse: collapse;
    border-spacing: 0;
}

product.html

<!DOCTYPE html>
<html lang="en">
<head>
  <!-- 
    normalize.css removes cross-browser differences in defaults, e.g.,
    differences in how form elements appear between Firefox and IE
    See: http://necolas.github.com/normalize.css/
  -->
  <link rel="stylesheet" href="normalize.css">

  <!-- Put your challenge-specific CSS in here -->
  <link rel="stylesheet" href="main.css">
  <title></title>
</head>
<body>
  <div class="container">
    <header>
      <h1>My Super SaaS</h1>
    </header>
    <nav>
      <ul>
        <li><a href="#">Home</a></li>
        <li><a href="#">Tour</a></li>   
        <li><a href="#">Pricing</a></li>
        <li><a href="#">About</a></li>
        <li><a href="#">Contact</a></li>
      </ul>
      <br clear="all">
    </nav>
    <div class="content">
      <h2>You are so totally going to love this application.</h2>
      <div id="registration">
        <form name="sign_up" action="#" method="post">
          <label for="email">Email</label>
          <input type="text" name="email">
          <label for="password">Password</label>
          <input type="password" name="password">

          <button type="submit">Sign Up</button>
        </form>
      </div>
      <div id="buzz">
        <h3>Check out our buzz:</h3>
        <blockquote>
          Probably the coolest thing I've ever seen in my entire life.
          <br><cite>- Ghandi</cite>
        </blockquote>
        <blockquote>
          I can't believe I ever got by without this.  What a lifesaver!
          <br><cite>- Cleopatra</cite>
        </blockquote>
        <blockquote>
          This is the most amazing creation ever imagined by humanity.
          <br><cite>- Some guy on the street</cite>
        </blockquote>
      </div>
      <div id="tour">
        <h2>Tour</h2>
        <h3>Some of the super features</h3>
        <div class="feature">
          <h4>Zip</h4>
          <img src="http://f.cl.ly/items/3e332b2e0B3d311a1U1X/wargames.jpg">
          <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
          <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
        </div>
        <div class="feature">
          <h4>Zap</h4>
          <img src="http://f.cl.ly/items/2h0Q3P0t0B3Q0N370u43/businessdude.jpg">
          <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
          <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
        </div>
        <div class="feature">
          <h4>Zop</h4>
          <img src="http://f.cl.ly/items/3i2V2V0D3n293d0y2y0U/tron.jpg">
          <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
          <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
        </div>
      </div>
      <div id="pricing">
        <h2>Pricing</h2>
        <dl>
          <dt>Basic</dt>
          <dd>$19.99 / mo.</dd>
          <dt>Pro</dt>
          <dd>$39.99 / mo.</dd>
          <dt>Platinum</dt>
          <dd>$99.99 / mo.</dd>
        </dl>
      </div>
      <div id="about">
        <h2>About</h2>
        <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
        <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
      </div>
      <div id="contact">
        <h2>Contact</h2>
        <table>
          <tbody>
            <tr>
              <td>Email</td>
              <td>supersass@example.com</td>
            </tr>
            <tr>
              <td>Twitter</td>
              <td>@supersass</td>
            </tr>
            <tr>
              <td>Phone</td>
              <td>555-867-5309</td>
            </tr>
          </tbody>
        </table>
      </div>
    </div>
    <div class="footer">
      Copyright &copy; 2013 Awesome People, Inc.
    </div>
  </div>
</body>
</html>