FrontendHaltCSS·Advanced·Coding·1 min read
What happens when var(--missing) references a custom property that was never defined, with no fallback given?
Short interview answer
The property using var() computes to its inherited or initial value, depending on whether it's an inherited property, effectively invalid at computed-value time for that declaration; providing a second argument to var() as a fallback avoids relying on that behavior and keeps the rule predictable.
Example
color: var(--brand, #e2521f); /* fallback used if --brand is undefined */Key takeaway
Explain the underlying mental model clearly, then support it with a concrete example and its trade-offs.