CSS Cascade Layers & !important: The Specificity Inversion

The Specificity Inversion

CSS Cascade Layers (@layer) are designed to solve specificity wars by allowing you to define explicit priority orders. The rule is simple: later layers override earlier layers, regardless of selector specificity. But there's shorter-but-deadlier catch: !important completely inverts this order.

If you use !important in an early layer (like a "reset" or "base" layer), it will override !important declarations in later layers (like "utilities" or "components"). This behavior is intentional—it preserves the "origin" balance—but it destroys the intuition that "later layers win."

The Mechanism

How Specificity normally works

In standard CSS cascading, layers sit between "Origin" (User/Author) and "Specificity" in importance. The standard order (lowest to highest priority) is:

• Unlayered styles (highest priority)
• Layer N (last declared)
• ...
• Layer 1 (first declared)

How !important specificy works

When !important is involved, the cascade origins are re-balanced. The browser creates a corresponding "important" origin for each standard origin, but in reverse order.

• Layer 1 !important (HIGHEST priority)
• ...
• Layer N !important
• Unlayered !important (lowest priority among importances)

Production Scenario: The Library Trap

Imagine you import a third-party UI library into a "framework" layer to ensure your custom styles (in an "overrides" layer) always win. This works perfectly for normal properties.

However, if that library uses !important for a utility class (e.g., .hidden { display: none !important; }), and you try to override it in your "overrides" layer with your own !important, you will fail. The library's !important is in an earlier layer, so it wins.

Code Demonstration

/* Define layer order */
@layer base, components, utilities;

/* 1. Base layer (First defined) */
@layer base {
  button {
    background: blue !important; /* WINS! */
    padding: 10px;
  }
}

/* 2. Utilities layer (Last defined) */
@layer utilities {
  button {
    background: red !important; /* LOSES */
    padding: 20px; /* WINS (normal cascading) */
  }
}

In this example, the background will be blue because @layer base is earlier, giving its !important higher priority. However, the padding will be 20px because for normal rules, the later layer (utilities) wins.

Interactive Demo

Explore how specificity inversion works in practice: