Glassmorphism emerged as a significant UI design trend around 2020, gaining widespread recognition when Apple adopted frosted glass effects extensively in macOS Big Sur and iOS design. The aesthetic draws inspiration from real-world frosted glass, creating a sense of depth and layering by allowing elements to appear translucent while blurring the content behind them. The term "glassmorphism" was popularized by the design community, particularly through Michal Malewicz's UXDesign article, as a successor to previous design trends like flat design, Material Design, and neumorphism.

The CSS backdrop-filter property is the core technology enabling glassmorphism effects. Unlike the filter property, which applies visual effects to an element and its contents, backdrop-filter applies effects to the area behind the element. The blur() function within backdrop-filter creates the characteristic frosted glass effect by applying a Gaussian blur to everything visible through the element's background. Typical glassmorphism implementations combine backdrop-filter: blur() with a semi-transparent background color (using rgba() or hsla() with low opacity), a subtle border (often 1px solid with a semi-transparent white), and a box-shadow for depth.

The rendering pipeline for backdrop-filter involves several compositing steps that affect performance. The browser must first render everything behind the element to an offscreen buffer, apply the specified filter effects to that buffer, then composite the filtered result with the element's own background and content. This process is GPU-accelerated on modern browsers but remains computationally intensive compared to simple solid backgrounds. Large blur values increase the sampling radius and computational cost, multiple layered glassmorphic elements multiply the compositing operations, and animations that change blur values force continuous recomposition. Designers should use glassmorphism judiciously, limiting the number of simultaneous glass elements and keeping blur values moderate (typically 10-20 pixels) for optimal performance.

Accessibility and usability considerations are important when implementing glassmorphism. The transparency and blur effects can reduce text readability, particularly for users with visual impairments, low contrast sensitivity, or in challenging viewing conditions like bright sunlight. Text over glassmorphic backgrounds must maintain sufficient contrast ratios per WCAG guidelines, which often requires increasing font weight, using darker text colors, or adding a stronger semi-transparent overlay to ensure readability. The saturate() filter function, sometimes combined with backdrop-filter to increase color vibrancy of the blurred background, can further complicate contrast calculations. Progressive enhancement ensures that browsers lacking backdrop-filter support (which has been universal in major browsers since 2022) receive a solid fallback background that maintains usability.