Use lit motion

src/components/ha-icon-button-group.ts

@@ -1,11 +1,89 @@
-import type { TemplateResult } from "lit";
+import { animate } from "@lit-labs/motion";
 import { css, html, LitElement } from "lit";
-import { customElement } from "lit/decorators";
+import { customElement, state } from "lit/decorators";
+import { classMap } from "lit/directives/class-map";
+import { styleMap } from "lit/directives/style-map";
+
+const THUMB_SIZE = 40;
 
 @customElement("ha-icon-button-group")
 export class HaIconButtonGroup extends LitElement {
-  protected render(): TemplateResult {
-    return html`<slot></slot>`;
+  @state() private _thumbX = 0;
+
+  @state() private _thumbVisible = false;
+
+  @state() private _thumbBorderOnly = false;
+
+  // When the thumb appears, only fade it in at its new position instead of
+  // also sliding it from wherever it was last visible.
+  private _thumbAppearing = false;
+
+  private _observer = new MutationObserver(() => this._updateThumb());
+
+  public disconnectedCallback(): void {
+    super.disconnectedCallback();
+    this._observer.disconnect();
+  }
+
+  protected render() {
+    return html`
+      <div
+        class="thumb ${classMap({
+          visible: this._thumbVisible,
+          "border-only": this._thumbBorderOnly,
+        })}"
+        style=${styleMap({ left: `${this._thumbX}px` })}
+        ${animate(() => ({
+          properties: this._thumbAppearing ? ["opacity"] : ["left", "opacity"],
+          keyframeOptions: {
+            duration: this._animationDuration(),
+            easing: "ease-in-out",
+          },
+          skipInitial: true,
+        }))}
+      ></div>
+      <slot @slotchange=${this._handleSlotchange}></slot>
+    `;
+  }
+
+  protected updated() {
+    this._thumbAppearing = false;
+  }
+
+  private _animationDuration(): number {
+    return (
+      parseFloat(
+        getComputedStyle(this).getPropertyValue("--ha-animation-duration-fast")
+      ) || 150
+    );
+  }
+
+  private _handleSlotchange(ev: Event) {
+    this._observer.disconnect();
+    const slot = ev.target as HTMLSlotElement;
+    for (const el of slot.assignedElements()) {
+      this._observer.observe(el, {
+        attributes: true,
+        attributeFilter: ["selected", "disabled"],
+      });
+    }
+    // Positions are only valid once the slotted buttons are laid out.
+    requestAnimationFrame(() => this._updateThumb());
+  }
+
+  private _updateThumb() {
+    const selected = this.querySelector<HTMLElement>(
+      "ha-icon-button-toggle[selected]:not([disabled])"
+    );
+    if (!selected) {
+      this._thumbVisible = false;
+      return;
+    }
+    this._thumbAppearing = !this._thumbVisible;
+    this._thumbBorderOnly = selected.hasAttribute("border-only");
+    this._thumbX =
+      selected.offsetLeft + (selected.offsetWidth - THUMB_SIZE) / 2;
+    this._thumbVisible = true;
   }
 
   static styles = css`
@@ -21,6 +99,32 @@ export class HaIconButtonGroup extends LitElement {
       width: auto;
       padding: 0;
     }
+    /* The selected toggle's circle is drawn here so it can slide between
+       toggles; their own circles are suppressed below. */
+    .thumb {
+      position: absolute;
+      top: calc(50% - 20px);
+      opacity: 0;
+      width: 40px;
+      height: 40px;
+      border-radius: var(--ha-border-radius-circle);
+      background-color: var(
+        --ha-icon-button-group-thumb-color,
+        var(--primary-text-color)
+      );
+      box-sizing: border-box;
+    }
+    .thumb.visible {
+      opacity: 1;
+    }
+    .thumb.border-only {
+      background-color: transparent;
+      border: 2px solid
+        var(--ha-icon-button-group-thumb-color, var(--primary-text-color));
+    }
+    ::slotted(ha-icon-button-toggle) {
+      --ha-icon-button-toggle-thumb-opacity: 0;
+    }
     ::slotted(.separator) {
       background-color: rgba(var(--rgb-primary-text-color), 0.15);
       width: 1px;

src/components/ha-icon-button-toggle.ts

@@ -44,8 +44,10 @@ export class HaIconButtonToggle extends HaIconButton {
         color: var(--primary-background-color);
         background-color: unset;
       }
+      /* ha-icon-button-group zeroes this so its sliding thumb draws the
+         circle instead. */
       :host([selected]:not([disabled])) ha-button::part(base)::before {
-        opacity: 1;
+        opacity: var(--ha-icon-button-toggle-thumb-opacity, 1);
       }
       ::slotted(*) {
         display: block;

src/dialogs/more-info/controls/more-info-light.ts

@@ -367,10 +367,10 @@ class MoreInfoLight extends LitElement {
           width: auto;
         }
         .wheel {
-          width: 30px;
-          height: 30px;
+          width: 28px;
+          height: 28px;
           flex: none;
-          border-radius: var(--ha-border-radius-xl);
+          border-radius: var(--ha-border-radius-circle);
         }
         .wheel.color {
           background-image: url("/static/images/color_wheel.png");