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The calc() function lets you perform basic math operations on values, and it’s especially useful when you need to add or subtract a length value from a percentage.

This is how it works:

div {
	max-width: calc(80% - 100px)
}

It returns a length value, so it can be used anywhere you expect a pixel value.

You can perform

  • additions using +
  • subtractions using -
  • multiplication using *
  • division using /

One caveat: with addition and subtraction, the space around the operator is mandatory, otherwise it does not work as expected.

Examples:

div {
	max-width: calc(50% / 3)
}
div {
	max-width: calc(50% + 3px)
}


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