Core class for registering and outputting CSS stylesheets.

Source: wp-includes/class-wp-styles.php
Since: 2.6.0
Extends: WP_Dependencies

Properties

Public Properties

Property	Type	Since	Description
$base_url	string	2.6.0	Base URL for styles (trailing slash)
$content_url	string	2.8.0	URL of wp-content directory
$default_version	string	2.6.0	Default version string
$text_direction	string	2.6.0	Text direction ('ltr' or 'rtl')
$concat	string	2.8.0	Handles to concatenate
$concat_version	string	2.8.0	Deprecated (3.4.0)
$do_concat	bool	2.8.0	Whether to concatenate
$print_html	string	2.8.0	HTML markup when concatenating
$print_code	string	3.3.0	Inline styles when concatenating
$default_dirs	array	2.8.0	Default style directories

Private Properties

Property	Type	Since	Description
$type_attr	string	5.3.0	Type attribute for style tags (empty for HTML5)

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Methods

__construct()

Initializes the styles object and fires initialization action.

public function __construct()

Since: 2.6.0

Behavior:

• Sets $type_attr to " type='text/css'" if theme doesn’t support HTML5 styles
• Fires wp_default_styles action

Hooks:

do_action_ref_array( 'wp_default_styles', array( &$this ) );

---

do_item()

Processes and outputs a single stylesheet.

public function do_item(
    string $handle,
    int|false $group = false
): bool

Since: 2.6.0

Parameter	Type	Description
$handle	string	Style handle
$group	int|false	Group level

Returns: true on success, false on failure.

Behavior:

• Skips styles with conditional comments
• Builds version query string
• Outputs inline styles after main stylesheet
• Handles RTL stylesheets when $text_direction is 'rtl'
• Applies style_loader_tag filter

RTL Handling:

• rtl => true or rtl => 'replace': Loads *-rtl.css (replaces original if 'replace')
• rtl => 'url': Loads specified RTL URL

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add_inline_style()

Adds inline CSS to a registered stylesheet.

public function add_inline_style(
    string $handle,
    string $code
): bool

Since: 3.3.0

Parameter	Type	Description
$handle	string	Style handle
$code	string	CSS code

Returns: true on success, false on failure.

Note: Inline styles are always added after the main stylesheet.

---

print_inline_style()

Prints inline styles for a handle.

public function print_inline_style(
    string $handle,
    bool $display = true
): string|bool

Since: 3.3.0

Parameter	Type	Description
$handle	string	Style handle
$display	bool	Print or return

Returns: false if no data, inline styles if $display true, true otherwise.

Note: Adds sourceURL comment for debugging when not concatenating.

---

add_data()

Adds data to a registered stylesheet with special handling for conditionals.

public function add_data(
    string $handle,
    string $key,
    mixed $value
): bool

Since: 6.9.0

Key	Effect
conditional	Clears dependencies (stylesheet will be ignored)

Returns: true on success, false on failure.

---

all_deps()

Determines all dependencies for given handles.

public function all_deps(
    string|string[] $handles,
    bool $recursion = false,
    int|false $group = false
): bool

Since: 2.6.0

Hooks:

$this->to_do = apply_filters( 'print_styles_array', $this->to_do );

---

_css_href()

Generates fully-qualified URL for a stylesheet.

public function _css_href(
    string $src,
    string $ver,
    string $handle
): string

Since: 2.6.0

Parameter	Type	Description
$src	string	Source URL or path
$ver	string	Version string
$handle	string	Style handle

Returns: Fully-qualified, escaped URL.

Hooks:

$src = apply_filters( 'style_loader_src', $src, $handle );

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in_default_dir()

Checks if source is in a default directory.

public function in_default_dir( string $src ): bool

Since: 2.8.0

Returns: true if in default directory.

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do_footer_items()

Processes styles enqueued late (in body).

public function do_footer_items(): string[]

Since: 3.3.0

Returns: Handles of processed styles.

Note: HTML5 allows styles in body; this outputs late-enqueued styles.

---

reset()

Resets concatenation properties.

public function reset(): void

Since: 3.3.0

Clears: do_concat, concat, concat_version, print_html

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get_dependency_warning_message()

Gets localized warning message for missing dependencies.

protected function get_dependency_warning_message(
    string $handle,
    string[] $missing_dependency_handles
): string

Since: 6.9.1

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Style Data Keys

Use wp_style_add_data() or $wp_styles->add_data():

Key	Type	Description
rtl	bool|string	RTL handling: true, 'replace', or URL
suffix	string	Suffix for RTL file (e.g., .min)
alt	bool	rel="alternate stylesheet"
title	string	Stylesheet title (for alternate)
path	string	Absolute path (enables inlining in 5.8.0+)
conditional	string	Deprecated, stylesheet ignored

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RTL Support Examples

Replace with RTL version

wp_register_style( 'my-style', 'css/style.css' );
wp_style_add_data( 'my-style', 'rtl', 'replace' );
// In RTL: loads css/style-rtl.css instead

Add RTL version alongside LTR

wp_register_style( 'my-style', 'css/style.css' );
wp_style_add_data( 'my-style', 'rtl', true );
// In RTL: loads both style.css AND style-rtl.css

Custom RTL URL

wp_register_style( 'my-style', 'css/style.css' );
wp_style_add_data( 'my-style', 'rtl', 'css/custom-rtl.css' );
// In RTL: loads custom-rtl.css

With suffix

wp_register_style( 'my-style', 'css/style.min.css' );
wp_style_add_data( 'my-style', 'rtl', 'replace' );
wp_style_add_data( 'my-style', 'suffix', '.min' );
// In RTL: loads css/style-rtl.min.css

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Alternate Stylesheets

wp_register_style( 'theme-dark', 'css/dark.css' );
wp_style_add_data( 'theme-dark', 'alt', true );
wp_style_add_data( 'theme-dark', 'title', 'Dark Mode' );
wp_enqueue_style( 'theme-dark' );
// Output: <link rel='alternate stylesheet' title='Dark Mode' ...>

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Inline Style Optimization (5.8.0+)

Stylesheets with a path set may be inlined if small enough:

wp_register_style( 'small-style', 'css/small.css' );
wp_style_add_data( 'small-style', 'path', ABSPATH . 'wp-content/themes/my-theme/css/small.css' );
// If file is small, contents are inlined instead of linked