The tan(angle) function accepts only one value as its parameter.

angle

A calculation which resolves to a <number> or an <angle>. When specifying unitless numbers they are interpreted as a number of radians, representing an <angle>.

The tangent of an angle will always return a number between −∞ and +∞.

• If angle is infinity, -infinity, or NaN, the result is NaN.
• If angle is 0⁻, the result is 0⁻.
• If angle is one of the asymptote values (such as 90deg, 270deg, etc.), the result is explicitly undefined. Authors must not rely on tan() returning any particular value for these inputs.

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

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

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

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

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

The tan() function can be used to draw a parallelogram with a given bounding box.

HTML

<div class="parallelogram"></div>

CSS

.parallelogram {
  --w: 400;
  --h: 200;
  --angle: 30deg;
  position: relative;
  width: calc(1px * var(--w));
  height: calc(1px * var(--h));
}
.parallelogram::before {
  content: "";
  position: absolute;
  width: calc(100% - 100% * var(--h) / var(--w) * tan(var(--angle)));
  height: 100%;
  transform-origin: 0 100%;
  transform: skewX(calc(0deg - var(--angle)));
  background-color: red;
}

Result

• sin()
• cos()
• asin()
• acos()
• atan()
• atan2()