Revision 998103 of CSS

<p><span class="seoSummary"><strong>Cascading Style Sheets</strong> (<strong>CSS</strong>) are a <a href="/en-US/docs/DOM/stylesheet">stylesheet</a> language used to describe the presentation of a document written in <a href="/en-US/docs/HTML" title="HyperText Markup Language">HTML</a></span> or <a href="/en-US/docs/XML">XML</a> (including XML dialects like <a href="/en-US/docs/SVG">SVG</a> or <a href="/en-US/docs/XHTML">XHTML</a>). CSS describes how elements should be rendered on screen, on paper, in speech, or on other media.</p>

<p>CSS is one of the core languages of the <em>open web</em> and has a standardized <a class="external" href="https://w3.org/Style/CSS/#specs">W3C specification</a>. Developed in levels, CSS1 is now obsolete, CSS2.1 is a recommendation, and <a href="/en-US/docs/CSS/CSS3" title="CSS3">CSS3</a>, now split into smaller modules, is progressing on the standardization track.</p>

<section id="sect1">
<ul class="card-grid">
 <li><span>CSS Reference</span>

  <p>An <a href="/en-US/docs/Web/CSS/Reference">exhaustive reference</a> for seasoned Web developers describing every property and concept of CSS.</p>
 </li>
 <li><span>CSS Tutorial</span>
  <p>A <a href="/en-US/docs/CSS/Getting_Started" title="Getting Started">step-by-step introduction</a> to help complete beginners get started. It presents all the needed fundamentals.</p>
 </li>
 <li><span>CSS3 Demos</span>
  <p>A <a href="/en-US/demos/tag/tech:css3">collection of demos</a> showing the latest CSS technologies in action: a boost for the creativity.</p>
 </li>
</ul>

<div class="row topicpage-table">
<div class="section">
<h2 class="Documentation" id="Documentation_and_tutorials">Documentation and tutorials</h2>

<dl>
 <dt>CSS key concepts</dt>
 <dd>Describes the <a href="/en-US/docs/CSS/Syntax">syntax and forms of the language</a> and introduces fundamentals like <a href="/en-US/docs/CSS/Specificity">specificity</a> and <a href="/en-US/docs/CSS/inheritance">inheritance</a>, the <a href="/en-US/docs/CSS/box_model">box model</a> and <a href="/en-US/docs/CSS/margin_collapsing">margin collapsing</a>, <a href="/en-US/docs/CSS/Understanding_z-index/The_stacking_context" title="The stacking context">stacking</a> and <a href="/en-US/docs/CSS/block_formatting_context" title="block formatting context">block-formatting</a> contexts, or the <a href="/en-US/docs/CSS/initial_value">initial</a>, <a href="/en-US/docs/CSS/computed_value">computed</a>, <a href="/en-US/docs/CSS/used_value">used</a>, and <a href="/en-US/docs/CSS/actual_value">actual</a> values. Entities like <a href="/en-US/docs/CSS/Shorthand_properties">CSS shorthand properties</a> are also defined.</dd>
 
<dt><a href="/en-US/docs/Web/Guide/CSS">CSS developer guide</a></dt>
 <dd>Articles to help you learn everything from the basics of styling HTML to assorted CSS techniques to make your content shine.</dd>

 <dt><a href="/en-US/docs/Web/CSS/Common_CSS_Questions">Common CSS questions</a></dt>
 <dd>Answers to common questions about CSS.</dd>
</dl>
</div>

<div class="section">
<h2 class="Tools" id="Tools_for_CSS_development">Tools for CSS development</h2>

<ul>
 <li>The <a class="external" href="https://jigsaw.w3.org/css-validator/">W3C CSS Validation Service</a> checks if CSS is valid. The service at <a href="https://www.onlinewebcheck.com/">OnlineWebCheck.com</a> also does the same. These are invaluable debugging tools.</li>
 <li><a href="/en-US/docs/Tools">Firefox Developer Tools</a> allow viewing and editing live CSS of a page via the <a href="/en-US/docs/Tools/Page_Inspector">Inspector</a> and <a href="/en-US/docs/Tools/Style_Editor">Style Editor</a> tools.</li>
 <li><a class="link-https" href="https://addons.mozilla.org/en-US/firefox/addon/1843">Firebug extension</a> for Firefox, a popular extension of that navigator that allows to edit live CSS on watched sites. Very practical to test some changes, though this extension does much more.</li>
 <li><a class="link-https" href="https://addons.mozilla.org/en-US/firefox/addon/60">Web Developer extension</a> for Firefox also allows to watch and edit live CSS on watched sites. Simpler than Firebug, though less powerful.</li>
 <li><a href="/en-US/docs/Web/CSS/Tools">Miscellaneous CSS tools.</a></li>
</ul>
</div>
</div>
</section>

<h2 id="See_also">See also</h2>

<ul>
 <li>Mozilla's <a href="/en-US/Learn/CSS">Learning CSS section</a></li>
 <li>Web languages CSS is often applied to: <a href="/en-US/docs/HTML">HTML</a>, <a href="/en-US/docs/SVG">SVG</a>, <a href="/en-US/docs/XHTML">XHTML</a> and <a href="/en-US/docs/XML">XML</a>.</li>
 <li>Mozilla technologies which make extensive use of CSS: <a href="/en-US/docs/Mozilla/Tech/XUL">XUL</a>, <a href="/en-US/Firefox">Firefox</a>, and <a href="/en-US/docs/Mozilla/Thunderbird">Thunderbird</a> <a href="/en-US/docs/Extensions">extensions</a> and <a href="/en-US/Add-ons/Themes">themes</a>.</li>
</ul>

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