Hsl() - CSS: Cascading Style Sheets - MDN Web Docs - Mozilla

Below are descriptions of the allowed values for both absolute and relative colors.

Absolute value syntax

hsl(H S L[ / A])

The parameters are as follows:

H

A <number>, an <angle>, or the keyword none (equivalent to 0deg in this case) representing the color's <hue> angle.

Note: The angles corresponding to particular hues differ across the sRGB (used by hsl() and hwb()), CIELAB (used by lch()), and Oklab (used by oklch()) color spaces. See the <hue> reference page for more detail and examples.

S

A <percentage> or the keyword none (equivalent to 0% in this case). This value represents the color's saturation. Here 100% is completely saturated, while 0% is completely unsaturated (gray).

L

A <percentage> or the keyword none (equivalent to 0% in this case). This value represents the color's lightness. Here 100% is white, 0% is black, and 50% is "normal".

A Optional

An <alpha-value> representing the alpha channel value of the color, where the number 0 corresponds to 0% (fully transparent) and 1 corresponds to 100% (fully opaque). Additionally, the keyword none can be used to explicitly specify no alpha channel. If the A channel value is not explicitly specified, it defaults to 100%. If included, the value is preceded by a slash (/).

Note: See Missing color components for more information on the effect of none.

Note: Absolute hsl() colors are serialized to rgb() values. The values of the red, green, and blue components may be rounded in serialization.

Relative value syntax

hsl(from <color> H S L[ / A])

The parameters are as follows:

from <color>

The keyword from is always included when defining a relative color, followed by a <color> value representing the origin color. This is the original color that the relative color is based on. The origin color can be any valid <color> syntax, including another relative color.

H

A <number>, an <angle>, or the keyword none (equivalent to 0deg in this case) representing the output color's <hue> angle.

S

A <percentage> or the keyword none (equivalent to 0% in this case). This represents the saturation of the output color. Here 100% is completely saturated, while 0% is completely unsaturated (gray).

L

A <percentage> or the keyword none (equivalent to 0% in this case). This represents the lightness of the output color. Here 100% is white, 0% is black, and 50% is "normal".

A Optional

An <alpha-value> representing the alpha channel value of the output color, where the number 0 corresponds to 0% (fully transparent) and 1 corresponds to 100% (fully opaque). Additionally, the keyword none can be used to explicitly specify no alpha channel. If the A channel value is not explicitly specified, it defaults to the alpha channel value of the origin color. If included, the value is preceded by a slash (/).

Note: To fully enable the representation of the full spectrum of visible colors, the output of relative hsl() color functions is serialized to color(srgb). That means that querying the output color value via the HTMLElement.style property or the CSSStyleDeclaration.getPropertyValue() method returns the output color as a color(srgb ...) value.

Defining relative color output channel components

When using relative color syntax inside an hsl() function, the browser converts the origin color into an equivalent HSL color (if it is not already specified as such). The color is defined as three distinct color channel values — h (hue), s (saturation), and l (lightness) — plus an alpha channel value (alpha). These channel values are made available inside the function to be used when defining the output color channel values:

• The h value is resolved to a <number> between 0 and 360, inclusive, that represents the origin color's <hue> degree value.
• The s and l values are each resolved to a <number> between 0 and 100, inclusive, where 100 is equivalent to 100%.
• The alpha value is resolved to a <number> between 0 and 1, inclusive.

When defining a relative color, the different channels of the output color can be expressed in several different ways. Below, we'll study some examples to illustrate these.

In the first two examples below, we are using relative color syntax. However, the first one outputs the same color as the origin color and the second one outputs a color not based on the origin color at all. They don't really create relative colors! You'd be unlikely to ever use these in a real codebase, and would probably just use an absolute color value instead. We included these examples as a starting point for learning about relative hsl() syntax.

Let's start with an origin color of rgb(255 0 0) (equivalent to hsl(0 100% 50%)). The following function outputs the same color as the origin color — it uses the origin color's h, s, and l channel values (0, 100%, and 50%) as the output channel values:

csshsl(from rgb(255 0 0) h s l)

This function's output color is the sRGB color() equivalent of hsl(0 100% 50%): color(srgb 1 0 0).

The next function uses absolute values for the output color's channel values, outputting a completely different color not based on the origin color:

csshsl(from rgb(255 0 0) 240 60% 70%)

In the above case, the output color is the sRGB color() equivalent of hsl(240 60% 70%): color(srgb 0.52 0.52 0.88).

The following function creates a relative color based on the origin color:

csshsl(from rgb(255 0 0) h 30% 60%)

This example:

• Converts the origin color (rgb(255 0 0)) into an hsl() equivalent (hsl(0 100% 50%)).
• Sets the H channel value for the output color to those of the origin color hsl() equivalent's H channel value — 0.
• Sets the output color's S and L channel values to new values not based on the origin color: 30% and 60%, respectively.

The final output color is the equivalent of hsl(0 30% 60%) in the sRGB color space — color(srgb 0.72 0.48 0.48).

Note: As mentioned above, if the output color is using a different color model to the origin color, the origin color is converted to the same model as the output color in the background so that it can be represented in a way that is compatible (i.e. using the same channels).

In the examples we've seen so far in this section, the alpha channels have not been explicitly specified for either the origin or output colors. When the output color alpha channel is not specified, it defaults to the same value as the origin color alpha channel. When the origin color alpha channel is not specified (and it is not a relative color), it defaults to 1. Therefore, the origin and output alpha channel values are 1 for the above examples.

Let's look at some examples that specify origin and output alpha channel values. The first one specifies the output alpha channel value as being the same as the origin alpha channel value, whereas the second one specifies a different output alpha channel value, unrelated to the origin alpha channel value.

csshsl(from rgb(255 0 0 / 0.8) h s l / alpha) /* Computed output color: color(srgb 1 0 0 / 0.8) */ hsl(from rgb(255 0 0 / 0.8) h s l / 0.5) /* Computed output color: color(srgb 1 0 0 / 0.5) */

In the following example, the rgb() origin color is again converted into an hsl() representation — hsl(0 100% 50% / 0.8). calc() calculations are applied to the H, S, L, and A values, and the final output color is the equivalent of hsl(60 80% 30% / 0.7) in the sRGB color space: color(srgb 0.72 0.72 0.08 / 0.7).

csshsl(from rgb(255 0 0 / 0.8) calc(h + 60) calc(s - 20) calc(l - 10) / calc(alpha - 0.1))

Note: Because the origin color channel values are resolved to <number> values, you have to add numbers to them when using them in calculations, even in cases where a channel would normally accept <percentage>, <angle>, or other value types. Adding a <percentage> to a <number>, for example, doesn't work.