The visually-hidden technique is the standard pattern for making content invisible without removing it from the accessibility tree. Crucially, it uses position: absolute, a 1x1 size, and clip: rect(0,0,0,0) rather than display: none, because display: none removes the element entirely; screen readers will not see it. Use this every time an icon-only button needs a label, or when you want extra context (like "opens in a new tab") that a sighted user does not need. The focusable variant is for skip-links: hidden by default, but visible when a keyboard user tabs to them, which is a baseline accessibility requirement.

These four hiding techniques behave very differently in layout, focus, and accessibility, and choosing the wrong one is a common bug. display: none removes the element entirely from both layout and the a11y tree; visibility: hidden keeps the layout slot but hides the content from sight and from screen readers; opacity: 0 is purely visual, so the element is still focusable and may still announce, which is why login forms that fade out a panel still trap keyboard focus inside the invisible element. aria-hidden="true" is the inverse of the visually-hidden recipe in accordion 1: visible to eyes, hidden to screen readers. Treat the comment block at the bottom as a quick lookup when you are deciding which to use.

filter is one of the highest-leverage CSS properties: a single declaration produces effects (blur, grayscale, sepia, drop-shadow, hue-rotate) that would otherwise need an SVG filter or a Canvas. The killer feature for icons is filter: drop-shadow(...) which respects the alpha channel of the rendered pixels, so a transparent SVG silhouette gets a shadow shaped like the silhouette, not its bounding box. backdrop-filter is the modern frosted-glass effect; it applies to the area behind the element, so it needs a translucent background to be visible. The catch is performance: every element with a filter becomes its own compositing layer, which costs GPU memory and can cause jank on low-end devices when applied to large or frequently-repainting elements.