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css-alpha-masking

Apply CSS alpha masking with linear-gradient for horizontal or vertical edge fades (mask-image and -webkit-mask-image). Use when asked for alpha masks, fade edges, or CSS mask gradients.

Published by MengTo ↗MengTo/Skills

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Fade a container's left and right edges

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Use the css-alpha-masking skill to provide CSS for a left/right edge fade on my supplied element. Use transparent edges with black stops at 15% and 85%, include both mask-image and -webkit-mask-image, and show where to apply the styles.

Required inputs

  • An element with visible content
  • The element's HTML and existing CSS

Suggested template by Skill Leaderboard, grounded in the linked source. Task evidence ↗

SKILL.md

name: css-alpha-maskingdescription: Apply CSS alpha masking with linear-gradient for horizontal or vertical edge fades (mask-image and -webkit-mask-image). Use when asked for alpha masks, fade edges, or CSS mask gradients.

CSS Alpha Masking Skill

Workflow

  1. Confirm direction (horizontal or vertical) and fade stop percentages.
  2. Provide the inline CSS snippet and any needed class usage.
  3. Offer small tweaks only (direction, stop positions, colors).

Usage checklist

  • Apply the mask styles directly on the element or in a CSS class.
  • Always include both mask-image and -webkit-mask-image for Safari.
  • Ensure the element has visible content; masks reveal/hide alpha only.

Horizontal (left/right) fade

/* Add this inline CSS to any element */
mask-image: linear-gradient(to right, transparent, black 15%, black 85%, transparent);
-webkit-mask-image: linear-gradient(to right, transparent, black 15%, black 85%, transparent);

Vertical (top/bottom) fade

/* Add this inline CSS to any element */
mask-image: linear-gradient(to bottom, transparent, black 15%, black 85%, transparent);
-webkit-mask-image: linear-gradient(to bottom, transparent, black 15%, black 85%, transparent);

Customization knobs

  • Direction: to right, to left, to bottom, to top.
  • Fade depth: adjust 15% and 85% stops.
  • Strength: change transparent to rgba(0,0,0,0.2) for softer fades.

Common pitfalls

  • Forgetting the -webkit-mask-image fallback in Safari.
  • Expecting masks to work on elements with overflow: hidden but no visible content behind.

Questions to ask when specs are missing

  • Which direction should the fade go?
  • How wide should the fade edges be?
  • Is this for images, text, or a container background?