Answer
Custom properties are author-defined CSS properties whose names begin with two hyphens. • Their values are substituted with the var() function. • They inherit by default and can vary by selector or media query. • Registered custom properties can define syntax, initial value, and inheritance behavior.
💡 Simple Example
:root { --space: 1rem; }
.card { padding: var(--space); }
⚡ Quick Revision
Custom properties create reusable values that still participate in the cascade.