After winning the top spot in the State of CSS 2023 survey as the "most anticipated new feature," the CSS if() function has finally received experimental browser implementations in 2025. It will allow conditional logic to be written inline within CSS property values, fundamentally changing the current approach of patching together conditional styles with CSS variables, media queries, and selectors.

Note: As of January 2025, if() is still at the CSS Working Group specification draft stage, available behind an experimental flag in Chrome but not yet stable.

Current Pain Points: Workarounds for Conditional Styles

/* Currently, writing conditional styles based on variables requires selector workarounds */
:root {
  --is-dark: 0; /* 0 or 1 */
}

/* Using calc() hack (only works for numeric values) */
.bg {
  /* (1 - var(--is-dark)) × 255 + var(--is-dark) × 0 */
  /* 0 → 255 (white), 1 → 0 (black) */
  background: rgb(
    calc((1 - var(--is-dark)) * 255),
    calc((1 - var(--is-dark)) * 255),
    calc((1 - var(--is-dark)) * 255)
  );
}

/* Or rely on CSS selectors :has()/:is() */
:root:has([data-theme="dark"]) .bg {
  background: black;
}
:root:not(:has([data-theme="dark"])) .bg {
  background: white;
}

CSS if() Syntax (Specification Draft)

/* Basic syntax */
.element {
  color: if(style(--variant: primary): blue; else: gray);
}

/* Multiple conditions */
.button {
  background: if(
    style(--size: large): hsl(200 80% 40%) ;
      style(--size: small): hsl(200 80% 60%) ; else: hsl(200 80% 50%)
  );

  padding: if(
    style(--size: large): 12px 24px; style(--size: small): 4px 8px; else: 8px
      16px
  );
}

/* Using media conditions */
.layout {
  display: if(media(width >= 768px): grid; else: flex);

  grid-template-columns: if(
    media(width >= 1024px): repeat(3, 1fr) ;
      media(width >= 768px): repeat(2, 1fr) ; else: 1fr
  );
}

/* Using supports conditions */
.animation {
  animation-timeline: if(
    supports(animation-timeline: scroll()): scroll() ; else: none
  );
}

if() Combined with Custom Properties: Component Variant System

This is the most powerful use case for if() — driving component variants purely through CSS variables without modifying HTML structure:

/* Define a button supporting variant and size variations */
.button {
  --variant: primary; /* default */
  --size: md;

  /* Use if() to determine all related properties based on variables */
  background: if(
    style(--variant: primary): var(--color-primary) ;
      style(--variant: secondary): transparent;
      style(--variant: danger): var(--color-danger) ; else: var(--color-primary)
  );

  color: if(style(--variant: secondary): var(--color-primary) ; else: white);

  border: if(
    style(--variant: secondary): 1px solid var(--color-primary) ; else: none
  );

  padding: if(
    style(--size: sm): 4px 10px; style(--size: lg): 12px 28px; else: 8px 16px
  );

  font-size: if(style(--size: sm): 13px; style(--size: lg): 17px; else: 15px);
}

<!-- Switch variants using only CSS variables -->
<button class="button" style="--variant: primary; --size: lg">
  Large Primary Button
</button>
<button class="button" style="--variant: secondary">Secondary Button</button>
<button class="button" style="--variant: danger; --size: sm">
  Small Danger Button
</button>

Comparison with Existing Approaches

Approach comparison (using "button variants" as an example, 3 variants × 3 sizes):

Approach                         Code volume   Dynamic switch   Runtime JS   Selector specificity
──────────────────────────────────────────────────────────────────────────────────────────────
CSS class names (.btn-primary-lg)  High          JS required      Yes          Accumulates
CSS variables + calc() hack        High          CSS variables    None         No effect
CSS selectors :has() combos        Moderate      CSS variables    None         Has effect
CSS if() (future)                  Low           CSS variables    None         No effect

How to Try It Now

# Chrome 125+ with experimental flag
# Enter in the address bar: chrome://flags
# Search: CSS if()
# Or: --enable-experimental-web-platform-features

/* Or use a PostCSS plugin for transformation (polyfill approach, partial compatibility) */
/* postcss-if-value and similar plugins are under development */

Summary

CSS if() represents the future direction of conditional logic in CSS — inlining component variant logic into CSS, reducing dependence on JavaScript, and making CSS variables a true "single source of truth" for themes and state. While it's not ready for production use in early 2025, it's worth understanding the syntax now so you can migrate quickly once it stabilizes.