The <calc-sum> CSS data type represents an expression which performs a calculation in any CSS math function. The expression executes a basic arithmetic operation of addition and subtraction between two values.
Syntax
The <calc-sum> type defines two numeric values and one of the following arithmetic operators between them.
+-
Adds two numbers together.
--
Subtracts the right number from the left.
Description
The operands in the expression may be any <length> syntax value. You can use <length>, <frequency>, <angle>, <time>, <percentage>, <number>, or <integer>.
Different unit types can be used in a single expression. For example, subtracting px from %, as in calc(100% - 10px), is a valid expression.
Including CSS variables in calc-sum expressions is also allowed. The following code calc(10px + var(--variable)), is a valid expression.
The + and - operators must be surrounded by whitespace. For instance, calc(50% -8px) will be parsed as a percentage followed by a negative length — an invalid expression — while calc(50% - 8px) is a percentage followed by a subtraction operator and a length. Likewise, calc(8px + -50%) is treated as a length followed by an addition operator and a negative percentage.