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Jakubantalik / transitions.dev

transitions-dev

Production-ready CSS transitions for web apps. Use when implementing notification badges, dropdowns, modals, panel reveals, page transitions, card resizes, number pop-ins, text swaps, icon swaps, success checks, avatar group hovers, error state shakes, search/input clear, skeleton loaders, shimmer text, sliding tabs, tooltips, staggered text reveals, card hover tilt, plus-to-menu morph, accordions, toasts, like buttons, learn-more hovers, checkbox checks, spinning counters, toggles, AI thinking states, reasoning streams, streaming text, matrix dot loaders, or banner stacking. Triggers on "add a transition", "animate the dropdown", "make the modal open smoothly", "swap icon", "page slide", "stagger animation", "open / close transition", "make it animate", "fade between", "success animation", "form error", "shake on invalid", "hover lift", "avatar stack hover", "clear the search", "skeleton loader", "loading shimmer", "shimmer text", "sliding tabs", "segmented control", "tooltip", "reveal text", "tilt card", "3D hover tilt", "cursor glare", "plus to menu", "FAB morph", "accordion", "collapsible", "expand / collapse", "disclosure", "toast", "snackbar", "like button", "heart animation", "learn more arrow", "checkbox", "check animation", "spinning counter", "odometer", "slot machine digits", "toggle", "switch", "thinking states", "AI status line", "agent reasoning", "reasoning stream", "streaming text", "stream words in", "matrix loader", "dot loader", "banner stack", "stacked toasts". Also "motion tokens", "scan for ad-hoc transitions", "replace hardcoded durations with motion tokens", "tokenize my animations", and the commands transitions reveal, transitions review, transitions apply, transitions refine.

View sourceMotionInteraction

Install

npx skills add https://github.com/Jakubantalik/transitions.dev --skill transitions-dev

Reasoning stream

When to use

An agent "thinking out loud" — a small card plays back a stream of reasoning by stepping the transcript up two lines at a time, holding between steps. Soft mask fades at the top and bottom edges sell "more above, more below", and the transcript is cloned once so the loop wraps without a visible jump.

Use for reasoning previews, live log tickers, changelog streams — any tall text that should scroll by inside a fixed viewport on its own clock.

HTML usage

html
<div class="t-reason">  <div class="t-reason-viewport">    <div class="t-reason-scroll">      <div class="t-reason-text">        <p>…transcript…</p>      </div>    </div>  </div></div>

The card clips a tall transcript; JS steps the scroll up --reason-lines lines every --reason-hold and clones .t-reason-text once so the offset can wrap by one copy's height mid-hold — the loop never shows a jump. The edge fades are a mask on the viewport (not gradients painted over the text), so the card background can be anything.

Tunable variables

VariableDefaultNotes
--reason-hold840mssourced from --p29-hold
--reason-step500mssourced from --p29-step-dur
--reason-lines2sourced from --p29-lines
--reason-fade28pxsourced from --p29-fade
--reason-easecubic-bezier(0.22, 1, 0.36, 1)sourced from --p29-ease

The :root defaults below match the live tuning on transitions.dev. Drop them into your global stylesheet once — every transition in this skill reads from semantic names like these, so multiple transitions can share a single :root block.

css
:root {  --reason-hold: 840ms;  --reason-step: 500ms;  --reason-lines: 2;  --reason-fade: 28px;  --reason-ease: cubic-bezier(0.22, 1, 0.36, 1);}

CSS

css
.t-reason { position: relative; overflow: hidden; }.t-reason-viewport {  position: absolute;  inset: 0;  overflow: hidden;  /* Edge fades are a mask, not painted gradients, so the card     background can be anything. */  -webkit-mask-image: linear-gradient(    transparent 0,    black var(--reason-fade),    black calc(100% - var(--reason-fade)),    transparent 100%);  mask-image: linear-gradient(    transparent 0,    black var(--reason-fade),    black calc(100% - var(--reason-fade)),    transparent 100%);}.t-reason-scroll {  position: absolute;  left: 0;  right: 0;  transform: translateY(0);  will-change: transform;}/* JS drives the tween:     scroll.style.transition = 'transform var(--reason-step) var(--reason-ease)';     scroll.style.transform  = 'translateY(-' + offset + 'px)';   and wraps the offset by one copy's height with transition: none. */
@media (prefers-reduced-motion: reduce) {  .t-reason-scroll { transition: none !important; transform: none !important; }}

The @media (prefers-reduced-motion: reduce) guard at the bottom of the snippet is required — keep it. It zeroes the transition for users who have asked for less motion at the OS level.

JavaScript orchestration

js
// Clone the transcript once so the wrap is seamless, then step the// scroll up --reason-lines lines every --reason-hold. The offset// wraps by one copy's height the moment a step lands past it — the// clone underneath makes the jump invisible.const scroll = document.querySelector(".t-reason-scroll");const text = scroll.querySelector(".t-reason-text");scroll.appendChild(text.cloneNode(true));
const num = (name, fb) => {  const v = parseFloat(    getComputedStyle(document.documentElement).getPropertyValue(name)  );  return Number.isFinite(v) ? v : fb;};
let offset = 0;(function step() {  setTimeout(() => {    const lineH = parseFloat(getComputedStyle(text).lineHeight) || 18;    const stepPx = lineH * num("--reason-lines", 2);    const dur = num("--reason-step", 500);    const ease = getComputedStyle(document.documentElement)      .getPropertyValue("--reason-ease").trim() || "ease-out";    offset += stepPx;    scroll.style.transition = "transform " + dur + "ms " + ease;    scroll.style.transform = "translateY(" + (-offset) + "px)";    setTimeout(() => {      const copyH = text.offsetHeight;      if (offset >= copyH) {        offset -= copyH;        scroll.style.transition = "none";        scroll.style.transform = "translateY(" + (-offset) + "px)";        void scroll.offsetWidth; // flush before the next tween      }      step();    }, dur + 30);  }, num("--reason-hold", 1200));})();