How Can I Debug CSS `calc()` Expression Errors and Computed Values?

Debug CSS calc() Expressions

1. Error Validation

CSS calc() formulas follow strict type checking rules:

• Same types for addition/subtraction (e.g., 5px 5px)
• One side a number for multiplication (e.g., 5px * 5)
• Right side a number for division (e.g., 5px / 5)
• White space on either side of and - operators

If any of these rules are violated, the expression becomes invalid.

2. Debugging the Computed Value

There is no direct way to get the computed value of a calc() expression. However, you can inspect the value applied to an element using:

JavaScript:

const elem = document.querySelector(".element");
const computedValue = getComputedStyle(elem).getPropertyValue("property-name");

Browser Developer Console:

• Inspect an element with the DevTools
• Click on the "Computed" panel
• Find the property that uses the calc() expression
• Hover over the value to see the computed result

Example:

.element {
  transform: scale(calc(var(--scale) * 1.2));
}

To debug:

• Inspect the ".element" element
• Check the "Computed" panel for the "transform" property
• Hover over the value (e.g., "scale(0.24)") to see the computed scale amount

Note: The computed value may vary based on the context it's used in, such as browser viewport size or element dimensions.

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