|$ curl https://forge-ai.dev/api/markdown?path=docs/css/filters
$cat docs/css-filters-&-blend-modes.md
updated Yesterday·10 min read·published
CSS Filters & Blend Modes
Introduction
CSS filters and blend modes bring image-editing capabilities directly to the browser. The filter property applies graphical effects like blur, contrast, and hue rotation to an element. The backdrop-filter applies these effects to the area behind an element. Blend modes (mix-blend-mode and background-blend-mode) control how elements visually blend with what is underneath them.
These properties enable sophisticated visual effects without JavaScript or image assets — terminal scanlines, glitch effects, frosted glass, color adjustments, and more can be achieved purely with CSS.
filters-intro.css
CSS
| 1 | .element { |
| 2 | filter: brightness(1.2) contrast(1.1) saturate(1.3); |
| 3 | /* Multiple filters can be chained — applied right to left */ |
| 4 | } |
Filter Functions
CSS provides ten filter functions that can be used individually or chained together. Each function accepts a parameter that controls the intensity of the effect.
| Function | Parameters | Description |
|---|---|---|
| blur() | length (px, rem) | Applies Gaussian blur |
| brightness() | number or % (0-∞) | Linear multiplier (0=black, 1=normal, >1=brighter) |
| contrast() | number or % (0-∞) | Adjusts contrast (0=gray, 1=normal, >1=more contrast) |
| grayscale() | number or % (0-1) | Converts to grayscale (0=color, 1=gray) |
| hue-rotate() | angle (deg, turn) | Rotates the hue (0deg=normal, 360deg=full circle) |
| invert() | number or % (0-1) | Inverts colors (0=normal, 1=inverted) |
| opacity() | number or % (0-1) | Applies transparency (0=transparent, 1=opaque) |
| saturate() | number or % (0-∞) | Adjusts saturation (0=desaturated, 1=normal) |
| sepia() | number or % (0-1) | Applies sepia tone (0=normal, 1=full sepia) |
| drop-shadow() | offset-x offset-y blur-radius color | Creates shadow following element contour |
filter-functions.css
CSS
| 1 | .blur { filter: blur(4px); } |
| 2 | .brightness { filter: brightness(1.5); } |
| 3 | .contrast { filter: contrast(2); } |
| 4 | .grayscale { filter: grayscale(100%); } |
| 5 | .hue-rotate { filter: hue-rotate(180deg); } |
| 6 | .invert { filter: invert(100%); } |
| 7 | .opacity { filter: opacity(0.5); } |
| 8 | .saturate { filter: saturate(3); } |
| 9 | .sepia { filter: sepia(100%); } |
| 10 | .drop-shadow { filter: drop-shadow(2px 4px 8px rgba(0,0,0,0.5)); } |
backdrop-filter
The backdrop-filter property applies filter effects to the area behind the element, creating effects like frosted glass. The element itself must be at least partially transparent for the effect to be visible.
backdrop-filter.css
CSS
| 1 | .glass { |
| 2 | background: rgba(13, 13, 13, 0.6); |
| 3 | backdrop-filter: blur(12px); |
| 4 | -webkit-backdrop-filter: blur(12px); /* Safari support */ |
| 5 | border: 1px solid rgba(255, 255, 255, 0.1); |
| 6 | } |
| 7 | |
| 8 | .glass-heavy { |
| 9 | background: rgba(26, 26, 46, 0.4); |
| 10 | backdrop-filter: blur(20px) saturate(1.5); |
| 11 | } |
| 12 | |
| 13 | /* Frosted terminal panel */ |
| 14 | .terminal-glass { |
| 15 | background: rgba(13, 13, 13, 0.7); |
| 16 | backdrop-filter: blur(8px); |
| 17 | border: 1px solid rgba(0, 255, 65, 0.1); |
| 18 | } |
⚠
warning
backdrop-filter can be performance-intensive, especially with high blur values or on low-powered devices. Use values between 4px-12px for a good balance of visual quality and performance. Always include the -webkit- prefix for Safari.
Multiple Filters
Multiple filter functions can be chained in a single filter declaration, separated by spaces. They are applied in order from right to left. Chaining filters creates compound effects that cannot be achieved with a single function.
multiple-filters.css
CSS
| 1 | .compound { |
| 2 | /* Apply brightness first, then grayscale */ |
| 3 | filter: grayscale(100%) brightness(1.2); |
| 4 | } |
| 5 | |
| 6 | .dramatic { |
| 7 | filter: contrast(1.5) saturate(1.3) sepia(0.3); |
| 8 | } |
| 9 | |
| 10 | .terminal-dark { |
| 11 | filter: brightness(0.8) contrast(1.2); |
| 12 | } |
| 13 | |
| 14 | .retro { |
| 15 | filter: sepia(0.6) hue-rotate(-20deg) saturate(1.4); |
| 16 | } |
| 17 | |
| 18 | /* Use variables to compose filters */ |
| 19 | .dim { --dim: brightness(0.7); } |
| 20 | .warm { --warm: sepia(0.3) saturate(1.3); } |
| 21 | .cool { --cool: hue-rotate(30deg) saturate(0.9); } |
| 22 | |
| 23 | .composed { |
| 24 | filter: var(--dim) var(--warm); |
| 25 | } |
blend-mode Properties
CSS supports two blend mode properties: mix-blend-mode blends an element with what is behind it, and background-blend-modeblends an element's background layers (images, gradients, colors) together.
blend-mode.css
CSS
| 1 | .mix-blend { |
| 2 | mix-blend-mode: multiply; /* multiplies colors — always darker */ |
| 3 | mix-blend-mode: screen; /* inverts, multiplies, inverts — always lighter */ |
| 4 | mix-blend-mode: overlay; /* combines multiply and screen */ |
| 5 | mix-blend-mode: difference; /* subtracts darker from lighter */ |
| 6 | mix-blend-mode: exclusion; /* similar to difference but lower contrast */ |
| 7 | } |
| 8 | |
| 9 | .background-blend { |
| 10 | background: |
| 11 | linear-gradient(45deg, #00FF41, #0D0D0D), |
| 12 | url('bg.png'); |
| 13 | background-blend-mode: overlay; |
| 14 | } |
| 15 | |
| 16 | /* Terminal overlay blend */ |
| 17 | .terminal-scanlines { |
| 18 | background: repeating-linear-gradient( |
| 19 | 0deg, |
| 20 | transparent, |
| 21 | transparent 2px, |
| 22 | rgba(0, 255, 65, 0.03) 2px, |
| 23 | rgba(0, 255, 65, 0.03) 4px |
| 24 | ); |
| 25 | mix-blend-mode: overlay; |
| 26 | pointer-events: none; |
| 27 | } |
mix-blend-mode
mix-blend-mode blends an element with its backdrop — the content behind it. It is commonly used for text overlays on images, creative hover effects, and terminal scanline overlays.
mix-blend-mode.css
CSS
| 1 | .text-overlay { |
| 2 | mix-blend-mode: difference; |
| 3 | color: white; |
| 4 | /* Text appears inverted against any background */ |
| 5 | } |
| 6 | |
| 7 | .image-text { |
| 8 | mix-blend-mode: overlay; |
| 9 | color: #0D0D0D; |
| 10 | font-weight: 900; |
| 11 | /* Text blends with background image */ |
| 12 | } |
| 13 | |
| 14 | /* Available mix-blend-mode values */ |
| 15 | /* |
| 16 | normal — no blending |
| 17 | multiply — multiplies pixel values (darker) |
| 18 | screen — inverse multiply (lighter) |
| 19 | overlay — combines multiply and screen |
| 20 | darken — uses darker pixel from each layer |
| 21 | lighten — uses lighter pixel from each layer |
| 22 | color-dodge — brightens backdrop |
| 23 | color-burn — darkens backdrop |
| 24 | hard-light — harsh lighting effect |
| 25 | soft-light — soft lighting effect |
| 26 | difference — subtracts darker from lighter |
| 27 | exclusion — similar to difference, lower contrast |
| 28 | hue — uses hue from element, saturation/luminosity from backdrop |
| 29 | saturation — uses saturation from element, hue/luminosity from backdrop |
| 30 | color — uses hue/saturation from element, luminosity from backdrop |
| 31 | luminosity — uses luminosity from element, hue/saturation from backdrop |
| 32 | */ |
background-blend-mode
background-blend-modeblends an element's multiple background layers together. It does not affect blending with content outside the element. This is useful for creating textured backgrounds, gradient overlays, and terminal CRT effects.
background-blend-mode.css
CSS
| 1 | .textured-bg { |
| 2 | background: |
| 3 | linear-gradient(135deg, #1A1A2E, #0D0D0D), |
| 4 | url('noise.png'); |
| 5 | background-blend-mode: overlay; |
| 6 | } |
| 7 | |
| 8 | /* Terminal CRT screen effect */ |
| 9 | .crt-screen { |
| 10 | background: |
| 11 | radial-gradient(ellipse at center, rgba(0, 255, 65, 0.1) 0%, transparent 70%), |
| 12 | #0D0D0D; |
| 13 | background-blend-mode: screen; |
| 14 | } |
| 15 | |
| 16 | /* Gradient on image */ |
| 17 | .image-overlay { |
| 18 | background: |
| 19 | linear-gradient(rgba(0, 255, 65, 0.3), rgba(0, 0, 0, 0.8)), |
| 20 | url('photo.jpg'); |
| 21 | background-blend-mode: multiply; |
| 22 | background-size: cover; |
| 23 | } |
Practical Filter Effects
Terminal Scanlines
terminal-scanlines.css
CSS
| 1 | .terminal-scanlines { |
| 2 | position: relative; |
| 3 | } |
| 4 | |
| 5 | .terminal-scanlines::after { |
| 6 | content: ''; |
| 7 | position: absolute; |
| 8 | inset: 0; |
| 9 | background: repeating-linear-gradient( |
| 10 | 0deg, |
| 11 | transparent 0px, |
| 12 | transparent 2px, |
| 13 | rgba(0, 255, 65, 0.03) 2px, |
| 14 | rgba(0, 255, 65, 0.03) 4px |
| 15 | ); |
| 16 | pointer-events: none; |
| 17 | mix-blend-mode: overlay; |
| 18 | } |
Glitch Effect
glitch.css
CSS
| 1 | .glitch { |
| 2 | position: relative; |
| 3 | color: #E0E0E0; |
| 4 | } |
| 5 | |
| 6 | .glitch::before, |
| 7 | .glitch::after { |
| 8 | content: attr(data-text); |
| 9 | position: absolute; |
| 10 | inset: 0; |
| 11 | opacity: 0.8; |
| 12 | } |
| 13 | |
| 14 | .glitch::before { |
| 15 | color: #FF0000; |
| 16 | animation: glitch-shift 0.3s infinite linear alternate; |
| 17 | clip-path: inset(20% 0 60% 0); |
| 18 | } |
| 19 | |
| 20 | .glitch::after { |
| 21 | color: #00FFFF; |
| 22 | animation: glitch-shift 0.3s infinite linear alternate-reverse; |
| 23 | clip-path: inset(60% 0 20% 0); |
| 24 | } |
| 25 | |
| 26 | @keyframes glitch-shift { |
| 27 | 0% { transform: translate(0); } |
| 28 | 20% { transform: translate(-2px, 1px); } |
| 29 | 40% { transform: translate(2px, -1px); } |
| 30 | 60% { transform: translate(-1px, 2px); } |
| 31 | 80% { transform: translate(1px, -2px); } |
| 32 | 100% { transform: translate(0); } |
| 33 | } |
Color Adjustments
color-adjustments.css
CSS
| 1 | .dark-mode-img { |
| 2 | filter: brightness(0.8) contrast(1.2); |
| 3 | /* Makes images consistent in dark mode */ |
| 4 | } |
| 5 | |
| 6 | .terminal-green { |
| 7 | filter: sepia(1) hue-rotate(70deg) saturate(3); |
| 8 | /* Converts any image to terminal green palette */ |
| 9 | } |
| 10 | |
| 11 | .hover-colorize { |
| 12 | filter: grayscale(100%); |
| 13 | transition: filter 0.3s ease; |
| 14 | } |
| 15 | |
| 16 | .hover-colorize:hover { |
| 17 | filter: grayscale(0%); |
| 18 | /* Desaturated by default, colorizes on hover */ |
| 19 | } |
| 20 | |
| 21 | /* Terminal CRT curvature effect */ |
| 22 | .crt-curvature { |
| 23 | filter: brightness(0.95) contrast(1.1); |
| 24 | background: radial-gradient( |
| 25 | ellipse at center, |
| 26 | transparent 60%, |
| 27 | rgba(0, 0, 0, 0.3) 100% |
| 28 | ); |
| 29 | } |
Best Practices
◆Chain multiple filters for compound effects — apply most expensive filters last
◆Use backdrop-filter sparingly — high blur values are performance-intensive
◆Always include -webkit-backdrop-filter for Safari compatibility
◆Use drop-shadow() instead of box-shadow when you need shadows that follow element contours
◆Combine filters with transitions for smooth interactive effects
◆Use mix-blend-mode for creative text overlays on image backgrounds
◆Multiply or overlay blend modes work well for darkening images with text overlays
◆Test filter-heavy designs on low-powered devices to ensure smooth performance
◆Filters create new stacking contexts — be aware of z-index implications
$Blueprint — Engineering Documentation·Section ID: CSS-25·Revision: 1.0
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