acos()

Baseline 2023

Newly available

Since March 2023, this feature works across the latest devices and browser versions. This feature might not work in older devices or browsers.

The acos()CSS function is a trigonometric function that returns the inverse cosine of a number between -1 and 1. The function contains a single calculation that returns the number of radians representing an <angle> between 0deg and 180deg.

Syntax

css

/* Single <number> values */ transform: rotate(acos(-0.2)); transform: rotate(acos(2 * 0.125)); /* Other values */ transform: rotate(acos(pi / 5)); transform: rotate(acos(e / 3));

Parameters

The acos(number) function accepts only one value as its parameter.

number: A calculation which resolves to a <number> between -1 and 1.

Return value

The inverse cosine of an number will always return an <angle> between 0deg and 180deg.

If number is less than -1 or greater than 1, the result is NaN.
If number is exactly 1, the result is 0.

Formal syntax

<acos()> = 
acos(<calc-sum>)

<calc-sum> = 
<calc-product>[[ '+' | '-' ]<calc-product>]*

<calc-product> = 
<calc-value>[[ '*' | / ]<calc-value>]*

<calc-value> = 
<number>|
<dimension>|
<percentage>|
<calc-keyword>|
 ( <calc-sum>)

<calc-keyword> = 
e|
pi|
infinity|
-infinity|
NaN

Examples

Rotate elements

The acos() function can be used to rotate elements as it return an <angle>.

HTML

html

<div class="box box-1"></div> <div class="box box-2"></div> <div class="box box-3"></div> <div class="box box-4"></div> <div class="box box-5"></div>

CSS

body { height: 100vh; display: flex; justify-content: center; align-items: center; gap: 50px; }

css

div.box { width: 100px; height: 100px; background: linear-gradient(orange, red); } div.box-1 { transform: rotate(acos(1)); } div.box-2 { transform: rotate(acos(0.5)); } div.box-3 { transform: rotate(acos(0)); } div.box-4 { transform: rotate(acos(-0.5)); } div.box-5 { transform: rotate(acos(-1)); }

Result

Specifications

Specification
CSS Values and Units Module Level 4 # trig-funcs