fix: small header on scroll

js/components/site-header.js

@@ -1,15 +1,52 @@
 /**
  * Site Header Component
  * Sticky header container that holds top-bar, navigation, and search
+ * Collapses on scroll down, expands on scroll up
+ * Based on: https://stackoverflow.com/questions/63902512/
  */
 class SiteHeader extends HTMLElement {
   constructor() {
     super();
     this.attachShadow({ mode: "open" });
+    this.prevScrollPos = 0;
+    this.headerOffset = 0;
+    this.collapsibleHeight = 0;
+    this.handleScroll = this.handleScroll.bind(this);
   }
 
   connectedCallback() {
     this.render();
+    this.collapsible = this.shadowRoot.querySelector(".collapsible");
+    window.addEventListener("scroll", this.handleScroll, { passive: true });
+  }
+
+  disconnectedCallback() {
+    window.removeEventListener("scroll", this.handleScroll);
+  }
+
+  handleScroll() {
+    const currentScrollPos = window.scrollY;
+    const isScrollingDown = currentScrollPos > this.prevScrollPos;
+    const delta = currentScrollPos - this.prevScrollPos;
+
+    if (!this.collapsibleHeight && this.collapsible) {
+      this.collapsibleHeight = this.collapsible.scrollHeight;
+    }
+
+    if (isScrollingDown) {
+      this.headerOffset = Math.min(
+        this.collapsibleHeight,
+        Math.max(0, this.headerOffset + delta)
+      );
+      this.classList.remove("reveal");
+    } else if (delta < 0) {
+      this.headerOffset = 0;
+      this.classList.add("reveal");
+    }
+
+    this.collapsible.style.transform = `translateY(-${this.headerOffset}px)`;
+
+    this.prevScrollPos = currentScrollPos;
   }
 
   render() {
@@ -20,17 +57,40 @@ class SiteHeader extends HTMLElement {
           position: sticky;
           top: 0;
           z-index: 100;
-          background-color: var(--color-background, #ffffff);
+          background-color: transparent;
         }
 
         .header {
           display: flex;
           flex-direction: column;
+          overflow: hidden;
+        }
+
+        .collapsible {
+          position: relative;
+          z-index: 1;
+          overflow: hidden;
+          transform: translateY(0);
+          transition: none;
+          will-change: transform;
+        }
+
+        :host(.reveal) .collapsible {
+          transition: transform 220ms ease;
+        }
+
+        ::slotted(top-bar) {
+          position: relative;
+          z-index: 2;
           border-bottom: 1px solid var(--color-border, #e2e8f0);
         }
       </style>
       <header class="header">
-        <slot></slot>
+        <slot name="top-bar"></slot>
+        <div class="collapsible">
+          <slot name="nav"></slot>
+          <slot name="search"></slot>
+        </div>
       </header>
     `;
   }