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Update documentation for forced colors mode #2819

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Update documentation for forced colors mode #2819

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3796608
Update documentation for forced colors mode
dlibby- Mar 3, 2021
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Address feedback
dlibby- Mar 5, 2021
192b942
Clarify system colors and modify wording
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dlibby- Mar 16, 2021
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53 changes: 32 additions & 21 deletions files/en-us/web/css/@media/forced-colors/index.html
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Expand Up @@ -12,10 +12,6 @@

<p><span class="seoSummary">The <strong><code>forced-colors</code></strong> <a href="/en-US/docs/Web/CSS">CSS</a> <a href="/en-US/docs/Web/CSS/Media_Queries/Using_media_queries#Media_features">media feature</a> is used to detect if the {{Glossary("user agent")}} has enabled a forced colors mode where it enforces a user-chosen limited color palette on the page.</span></p>
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<div class="notecard note">
<p><strong>Note:</strong> This feature is not supported by any user agent and its specifics are subject to change.</p>
</div>

<h2 id="Syntax">Syntax</h2>

<p>The <code>forced-colors</code> media feature indicates whether or not the browser is currently in forced-colors mode.</p>
Expand All @@ -26,60 +22,75 @@ <h3 id="Values">Values</h3>
<dt><code><dfn>none</dfn></code></dt>
<dd>Forced colors mode is not active; the page’s colors are not being forced into a limited palette.</dd>
<dt><code>active</code></dt>
<dd>Indicates that forced colors mode is active. The browser provides the color palette to authors through the <a href="/en-US/docs/Web/CSS/color_value#System_Colors">CSS system color</a> keywords and, if appropriate, it triggers the appropriate value of <code><a href="/en-US/docs/Web/CSS/@media/prefers-color-scheme">prefers-color-scheme</a></code> so that authors can adapt the page.</dd>
<dd>Indicates that forced colors mode is active. The browser provides the color palette to authors through the <a href="/en-US/docs/Web/CSS/color_value#System_Colors">CSS system color</a> keywords and, if appropriate, triggers the appropriate value of <code><a href="/en-US/docs/Web/CSS/@media/prefers-color-scheme">prefers-color-scheme</a></code> so that authors can adapt the page.</dd>
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</dl>

<h2 id="Usage_notes">Usage notes</h2>

<h3 id="Properties_affected_by_forced-color_mode">Properties affected by forced-color mode</h3>

<p>In forced colors mode, the values of the following properties are treated as if they have no author-level values specified. That is, user-specified values (if any) or browser-specified values are used instead.</p>
<p>In forced colors mode, the values of the following properties are treated as if they have no author-level values specified. That is, browser-specified values are used instead. This does not affect the style cascade, but is accomplished by the browser using the browser-specified values instead of the cascaded values when painting colors. These browser-specified values are selected from the set of system colors &emdash; this ensures a consistent contrast for common UI elements for users that have forced colors enabled.</p>
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<ul>
<li>{{cssxref("color")}}</li>
<li>{{cssxref("background-color")}}</li>
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<li>{{cssxref("text-decoration-color")}}</li>
<li>{{cssxref("text-emphasis-color")}}</li>
<li>{{cssxref("border-color")}}</li>
<li>{{cssxref("outline-color")}}</li>
<li>{{cssxref("column-rule-color")}}</li>
<li>{{cssxref("scrollbar-color")}}</li>
<li>{{cssxref("-webkit-tap-highlight-color")}}</li>
<li>{{cssxref("box-shadow")}}</li>
<li>{{cssxref("text-shadow")}}</li>
<li><a href="/en-US/docs/Web/SVG/Attribute/fill">SVG fill attribute</a></li>
<li><a href="/en-US/docs/Web/SVG/Attribute/stroke">SVG stroke attribute</a></li>
</ul>

<p>You can use <a href="/en-US/docs/Web/CSS/color_value#System_Colors">system color keywords</a> with any property <em>other</em> than those listed above, to ensure that the rest of the page integrates with the restricted color palette available in forced colors mode.</p>
<p>Additionally the following properties have special behavior in forced colors mode:</p>
<ul>
<li>{{cssxref("box-shadow")}} is forced to 'none'</li>
<li>{{cssxref("text-shadow")}} is forced to 'none'</li>
<li>{{cssxref("background-image")}} is forced to 'none' for values that are not url-based</li>
<li>{{cssxref("color-scheme")}} is forced to 'light dark'</li>
<li>{{cssxref("scrollbar-color")}} is forced to 'auto'</li>
</ul>

<p>The system colors that are forced for the above properties depend on the context of the element. For example the {{cssxref("color")}} property on button element will be forced to ButtonText, whereas on normal text it will be forced to CanvasText. See the list of system colors for additional details of when each might be appropriate in various UI contexts.</p>
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<p><strong>Note:</strong> user agents choose system colors based on elements, <em>not</em> their roles. As an example, adding role="button" to a div will not cause an element's color to be forced to ButtonText</p>
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<p>There are two cases where the user agent does not force the values for the above properties &emdash; when a {{cssxref("forced-color-adjust")}} value of 'none' is applied to an element, or when a system color is specified by the author.</p>
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<p>There are two cases where the user agent does not force the values for the above properties &emdash; when a {{cssxref("forced-color-adjust")}} value of 'none' is applied to an element, or when a system color is specified by the author.</p>
<p>There are two cases where the user agent does not force the values for the above properties &emdash; when a {{cssxref("forced-color-adjust")}} value of <code>none</code> is applied to an element, or when a system color is specified by the author.</p>

<p>When forced-color-adjust is set to 'none' on an element, none of the forced color values will apply, and author style will be applied as normal.</p>
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<p>When a system color is specified, it will be used instead of the value that would otherwise have been forced.</p>

<p>You can also use system colors with any property <em>other</em> than those listed above, to ensure that the rest of the page integrates with the restricted color palette available in forced colors mode.</p>

<h3 id="User_preferences">User preferences</h3>

<p>This media feature is active only if the user has enabled color scheme preferences in their operating system. For example High Contrast mode on Windows.</p>
<p>This media feature is active only if the user has enabled color scheme preferences in their operating system. One example of such a feature is High Contrast mode on Windows.</p>

<h2 id="Examples">Examples</h2>

<div class="notecard note">
<p><strong>Note:</strong> The below example will only work when using a browser that supports this media feature, and with a preference such as High Contrast mode enabled in your OS.</p>
</div>

<p>This example has an annoying color palette by default. This example does not take advantage of the colors provided by the user agent.</p>
<p>This example is a button that normally gets its contrast via {{cssxref("box-shadow")}}. Under forced colors mode, box-shadow is forced to none, so the example uses the forced-colors media feature to ensure there is a border of the appropriate color (ButtonText in this case)</p>

<h3 id="HTML">HTML</h3>

<pre class="brush: html">&lt;div class="colors"&gt;weird color box&lt;/div&gt;
<pre class="brush: html">&lt;button class="button"&gt;Press me!&lt;/button&gt;
</pre>

<h3 id="CSS">CSS</h3>

<pre class="brush: css">.colors {
background-color: red;
color: grey;
<pre class="brush: css">
.button {
border: 0;
padding: 10px;
box-shadow: -2px -2px 5px gray, 2px 2px 5px gray;
}

@media (forced-colors: active) {
.colors {
background-color: white;
color: black;
.button {
/* Use a border instead, since box-shadow is forced to 'none' in forced-colors mode */
border: 2px ButtonText solid;
}
}
</pre>
Expand Down Expand Up @@ -120,5 +131,5 @@ <h2 id="See_also">See also</h2>
<ul>
<li><a href="/en-US/docs/Web/CSS/@media">@media</a></li>
<li><a href="https://blogs.windows.com/msedgedev/2020/09/17/styling-for-windows-high-contrast-with-new-standards-for-forced-colors/">Styling for Windows high contrast with standards for forced colors.</a></li>
<li>{{cssxref("forced-color-adjust")}}</li>
<li>{{cssxref("forced-color-adjust")}}</li>
</ul>
12 changes: 6 additions & 6 deletions files/en-us/web/css/color_value/index.html
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Expand Up @@ -926,19 +926,19 @@ <h3 id="System_Colors">System Colors</h3>
</dd>
<dt>ButtonFace</dt>
<dd>
<p>Background of push buttons</p>
<p>Background color of controls</p>
</dd>
<dt>ButtonText</dt>
<dd>
<p>Text of push buttons</p>
<p>Foreground color of controls</p>
</dd>
<dt>Canvas</dt>
<dd>
<p>Background of application content or documents</p>
</dd>
<dt>CanvasText</dt>
<dd>
<p>Text in application content or documents</p>
<p>Text or foreground color in application content or documents</p>
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</dd>
<dt>Field</dt>
<dd>
Expand All @@ -950,15 +950,15 @@ <h3 id="System_Colors">System Colors</h3>
</dd>
<dt>GrayText</dt>
<dd>
<p>Text that is disabled</p>
<p>Text or foreground color for disabled items (e.g. a disabled control)</p>
</dd>
<dt>Highlight</dt>
<dd>
<p>Background of items that are selected in a control</p>
<p>Background of selected items</p>
</dd>
<dt>HighlightText</dt>
<dd>
<p>Text of items that are selected in a control</p>
<p>Text or foreground color of selected items</p>
</dd>
<dt>LinkText</dt>
<dd>
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