Beach is fixed width or fluid. There are several width options in the configuration settings and this page is set to fluid.

Download Beach from http://drupal.org/project/beach. This version is 6.x-1.0-beta1 from 2009-May-12, a 100.75 KB download.

You can set the page with in Administer > Site settings > Themes > Beach > Configure.
Container Width:
Narrow (Fixed width: 780px)
Medium (Fixed width: 840px)
Wide (Fixed width: 960px)
Super Wide (Fixed width: 1020px)
Extreme Wide (Fixed width: 1140px)
(.) Fluid (min-width: 780px)
Select the container width you need. Be careful, the Narrow and Medium Width may not suite 2 sidebars page.

The W3C and Total Validator pass this theme as XHTML 1.0 Strict. The theme passed WCAG (WAI) level A validation then failed AA validation with headings not properly nested.
<h3 class="hidden">Primary Menu</h3>

Wave did not detect accessibility errors.

CSS validation produces lots of warnings about proprietary settings. Here is the start of the CSS 2.1 report:
W3C CSS Validator results for http://d-theme.com/beach (CSS level 2.1)
Sorry! We found the following errors (64)
URI : http://d-theme.com/sites/all/themes/beach/css/framework/drupal6-core.css?k
815 tr.drag Property opacity doesn't exist in CSS level 2.1 but exists in [css3] : 0.5
URI : http://d-theme.com/sites/all/themes/beach/css/beach.css?k
205 #menu-bar Property -moz-border-radius-topleft doesn't exist : 1.5em
206 #menu-bar Property -webkit-border-top-left-radius doesn't exist : 1.5em
207 #menu-bar Property border-top-left-radius doesn't exist in CSS level 2.1 but exists in [css3] : 1.5em

Here is the start of the CSS 3 errors:
W3C CSS Validator results for http://d-theme.com/beach (CSS level 3)
Sorry! We found the following errors (43)
URI : http://d-theme.com/sites/all/themes/beach/css/framework/reset.css?k
39 blockquote:before, blockquote:after, q:before, q:after Value Error : content none is not a content value : none
URI : http://d-theme.com/sites/all/themes/beach/css/beach.css?k
205 #menu-bar Property -moz-border-radius-topleft doesn't exist : 1.5em
206 #menu-bar Property -webkit-border-top-left-radius doesn't exist : 1.5em
208 #menu-bar Property -moz-border-radius-topright doesn't exist : 1.5em

Example HTML

Here are example HTML elements to see how they are formatted by this theme.

<a href="?x">link 1</a>: link 1 This is a test of a link you have not visited. See how links are highlighted. Hover your mouse over this link to see any hover effects that might be used then select the link to see the link displayed as visited.

<a href="?y">link 2</a>: link 2 Leave this link unselected as a comparison link you have not visited.

<abbr title="abbreviation">abbr</abbr>: abbreviation

<acronym title="Cyclic Redundancy Checksum">CRC</acronym>: CRC

<blockquote>blockquote</blockquote>:

blockquote

<cite>cite</cite>: cite

<code>code</code>: code

<div>div</div>:

<form> and <input>: The the comments form at the end of this page (if you are logged in).

<em>em</em>: em

<h1>h1</h1> is usually the top heading in the page. Repeating h1 in this test would break heading nesting.

<h2>h2</h2>:

h2

<h3>h3</h3>:

h3

<h4>h4</h4>:

h4

<h5>h5</h5>:

h5

<h6>h6</h6>:

h6

<hr />:

<ol><li>li</li></ol>:

1. li

<p>paragraph</p>:

paragraph

<pre>.h3
      {
      font-size: 1.17em;
      }</pre>

.h3
      {
      font-size: 1.17em;
      }

<q>quote</q>: quote

<span>span</span>: span

<strong>strong</strong>: strong

<table><thead><tr><td>th1</td><td>th2</td></tr></thead>
<tbody>
<tr><td>td1</td><td>td2</td></tr>
<tr><td>td3</td><td>td4</td></tr>
</tbody>
</table>:

<ul><li>li</li><li>li</li></ul>:

• li
• li