Refresh website branding. (#16151)

Context: https://groups.google.com/g/iree-discuss/c/kdFr4CQwEyY

This is mostly a revert of https://github.com/openxla/iree/pull/12229,
moving back to mostly default colors and IREE icons. We can add back
custom colors etc. later (e.g.
https://squidfunk.github.io/mkdocs-material/setup/changing-the-colors/).

Current site: https://iree.dev/
Preview: https://scotttodd.github.io/iree/
diff --git a/docs/website/overrides/.icons/iree/ghost.svg b/docs/website/docs/assets/images/ghost.svg
similarity index 100%
rename from docs/website/overrides/.icons/iree/ghost.svg
rename to docs/website/docs/assets/images/ghost.svg
diff --git a/docs/website/docs/assets/images/openxla-logo-lockup-white.svg b/docs/website/docs/assets/images/openxla-logo-lockup-white.svg
deleted file mode 100644
index 6a0d1d1..0000000
--- a/docs/website/docs/assets/images/openxla-logo-lockup-white.svg
+++ /dev/null
@@ -1,44 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!-- Generator: Adobe Illustrator 26.3.1, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
-<svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
-	 viewBox="0 0 430 110" style="enable-background:new 0 0 430 110;" xml:space="preserve">
-<style type="text/css">
-	.st0{fill:#1C466C;}
-	.st1{fill:#5EA8DA;}
-	.st2{fill:#FFFFFF;}
-	.st3{fill:#203A5C;}
-	.st4{fill:none;stroke:#20FFC2;stroke-miterlimit:10;}
-	.st5{fill:none;stroke:#203A5C;stroke-miterlimit:10;}
-	.st6{fill:#3676DE;}
-	.st7{fill:#15273B;}
-	.st8{fill:#3775E0;}
-</style>
-<g>
-	<polygon class="st2" points="32.98,108.78 1.93,55 32.98,1.22 101.47,1.22 132.52,55 101.47,108.78 	"/>
-	<polygon class="st8" points="79.52,55 97.76,23.4 101.86,30.49 87.71,55 97.76,72.41 89.57,72.41 	"/>
-	<polygon class="st1" points="54.93,55 36.69,86.6 32.59,79.5 46.74,55 36.69,37.59 44.88,37.59 	"/>
-	<polygon class="st7" points="85.47,79.5 71.32,55 89.57,23.4 81.37,23.4 75.42,33.71 69.47,23.4 61.27,23.4 71.32,40.81 
-		67.22,47.9 53.08,23.4 36.69,23.4 32.59,30.49 48.98,30.49 63.13,55 44.88,86.6 53.08,86.6 59.03,76.29 64.98,86.6 73.18,86.6 
-		63.13,69.19 67.22,62.09 81.37,86.6 97.76,86.6 101.86,79.5 	"/>
-	<g>
-		<path class="st2" d="M165.17,55c0-13.87,8.79-22.72,21.59-22.72c12.8,0,21.53,8.85,21.53,22.72c0,13.74-8.72,22.72-21.53,22.72
-			C173.96,77.72,165.17,68.74,165.17,55z M199.75,55c0-9.41-5.02-14.94-12.99-14.94c-7.97,0-12.99,5.52-12.99,14.94
-			c0,9.22,5.02,15,12.99,15C194.73,70,199.75,64.23,199.75,55z"/>
-		<path class="st2" d="M246.19,60.33c0,11.3-5.71,17.38-13.93,17.38c-3.76,0-6.71-1.32-8.72-3.51v15.12h-8.03V52.87l-2.7-5.46
-			l7.78-3.95l2.2,4.58c2.26-2.7,5.71-4.9,10.36-4.9C241.24,43.14,246.19,49.73,246.19,60.33z M237.91,60.27
-			c0-6.28-2.82-9.98-8.28-9.98c-2.2,0-4.33,0.56-6.09,1.57v16.88c1.69,1.13,3.76,1.76,5.9,1.76
-			C234.71,70.5,237.91,66.86,237.91,60.27z"/>
-		<path class="st2" d="M280.4,61.65h-21.46c0.69,5.08,4.64,8.22,11.17,8.22c3.58,0,7.47-0.75,10.04-2.13l-2.45,8.03
-			c-2.26,1.25-5.65,1.95-9.73,1.95c-10.92,0-17.38-6.84-17.38-17.38c0-10.67,6.34-17.2,16.63-17.2c8.72,0,14,4.96,14,12.99
-			C281.21,57.89,280.96,60.08,280.4,61.65z M259.12,56.63h14.37c-0.25-4.83-2.45-6.9-6.28-6.9
-			C262.95,49.73,260.06,52.3,259.12,56.63z"/>
-		<path class="st2" d="M316.05,53.81v23.1h-8.03V57.01c0-4.33-1.76-6.59-5.9-6.59c-2.38,0-4.58,0.82-6.4,1.63V76.9h-8.03V52.8
-			l-2.7-5.77l7.78-3.7l2.51,5.15c3.64-3.26,7.41-5.27,11.23-5.27C312.66,43.2,316.05,46.84,316.05,53.81z"/>
-	</g>
-	<path class="st1" d="M358.03,33.1l-13.37,22.53l13.43,21.28h-9.54l-7.72-12.43l-1.57-3.64h-0.38l-1.44,3.58l-7.28,12.49h-9.29
-		l13.74-22.15L321.07,33.1h9.41l8.1,12.99l1.32,3.33h0.38l1.44-3.45l7.22-12.87H358.03z"/>
-	<path class="st1" d="M372.03,69.81h15.44v7.09h-23.6V33.1h8.16V69.81z"/>
-	<path class="st1" d="M419.66,76.9l-3.51-11.17h-15.12l-3.58,11.17h-8.28l14.31-43.81h10.35l14.25,43.81H419.66z M403.16,59.02
-		h10.86l-4.52-14.31l-0.69-3.39h-0.44l-0.69,3.39L403.16,59.02z"/>
-</g>
-</svg>
diff --git a/docs/website/docs/assets/stylesheets/openxla.css b/docs/website/docs/assets/stylesheets/iree.css
similarity index 75%
rename from docs/website/docs/assets/stylesheets/openxla.css
rename to docs/website/docs/assets/stylesheets/iree.css
index 7f67eb5..083fc31 100644
--- a/docs/website/docs/assets/stylesheets/openxla.css
+++ b/docs/website/docs/assets/stylesheets/iree.css
@@ -1,21 +1,5 @@
 @import url(//fonts.googleapis.com/icon?family=Material+Icons|Material+Icons+Outlined);
 
-[data-md-color-scheme="default"] {
-  --md-primary-fg-color: #1a344c; /* OpenXLA navy */
-  --md-typeset-a-color: #458ae5; /* OpenXLA blue 01 */
-  --md-accent-fg-color: #6fb6e0; /* OpenXLA blue 02 */
-}
-
-[data-md-color-scheme="slate"] {
-  --md-primary-fg-color: #1a344c; /* OpenXLA navy */
-  --md-typeset-a-color: #6fb6e0; /* OpenXLA blue 02 */
-  --md-accent-fg-color: #458ae5; /* OpenXLA blue 01 */
-  /* H1 color */
-  --md-default-fg-color--light: rgba(204, 234, 254, 0.6);
-  /* Button color */
-  --md-default-fg-color--lighter: rgba(204, 234, 254, 0.3);
-}
-
 .md-header__button.md-logo :is(img, svg),
 .md-header__button.md-logo :-webkit-any(img, svg) {
   height: 1.6rem;
diff --git a/docs/website/mkdocs.yml b/docs/website/mkdocs.yml
index d477146..071533c 100644
--- a/docs/website/mkdocs.yml
+++ b/docs/website/mkdocs.yml
@@ -6,7 +6,7 @@
 
 theme:
   name: material
-  logo: assets/images/openxla-logo-lockup-white.svg
+  logo: assets/images/ghost.svg
   logo_alt: IREE
   icon:
     repo: fontawesome/brands/github
@@ -14,9 +14,8 @@
   font:
     text: Noto
     code: Noto Sans Mono
-  favicon: assets/images/favicon.png
+  favicon: assets/images/ghost.svg
 
-  # Note: this includes symlinks to forked files in third_party/mkdocs-material/
   custom_dir: overrides
 
   features:
@@ -37,13 +36,13 @@
     - toc.follow # Scroll the TOC panel to follow the reader
 
   palette:
-    # Light mode (scheme overrides in openxla.css)
+    # Light mode
     - media: "(prefers-color-scheme: light)"
       scheme: default
       toggle:
         icon: material/brightness-7
         name: Switch to dark mode
-    # Dark mode (scheme overrides in openxla.css)
+    # Dark mode
     - media: "(prefers-color-scheme: dark)"
       scheme: slate
       toggle:
@@ -51,10 +50,6 @@
         name: Switch to light mode
 
 extra:
-  # TODO(scotttodd): https://openxla.github.io/community (when hosted)
-  community_homepage: https://github.com/openxla/community
-  community_site_name: OpenXLA
-
   homepage: https://iree.dev/
 
   # TODO(scotttodd): join mkdocs-material insiders and remove notice?
@@ -77,7 +72,7 @@
 
 extra_css:
   - assets/stylesheets/extra.css
-  - assets/stylesheets/openxla.css
+  - assets/stylesheets/iree.css
 
 copyright: Copyright &copy; 2024 The IREE Authors
 
@@ -114,7 +109,7 @@
       custom_checkbox: true
   - tables
   - toc:  # Table of Contents
-      permalink: 'link'  # Use Material font's "link" icon; see openxla.css
+      permalink: 'link'  # Use Material font's "link" icon; see iree.css
       toc_depth: 4
 
 # Navigation with explicit ordering and nesting.
diff --git a/docs/website/overrides/.icons/iree/ghost.svg b/docs/website/overrides/.icons/iree/ghost.svg
new file mode 120000
index 0000000..6674e9b
--- /dev/null
+++ b/docs/website/overrides/.icons/iree/ghost.svg
@@ -0,0 +1 @@
+../../../docs/assets/images/ghost.svg
\ No newline at end of file
diff --git a/docs/website/overrides/partials/header.html b/docs/website/overrides/partials/header.html
deleted file mode 120000
index 99ee450..0000000
--- a/docs/website/overrides/partials/header.html
+++ /dev/null
@@ -1 +0,0 @@
-../../../../third_party/mkdocs-material/overrides/partials/header.html
\ No newline at end of file
diff --git a/docs/website/overrides/partials/nav.html b/docs/website/overrides/partials/nav.html
deleted file mode 120000
index 4da8db8..0000000
--- a/docs/website/overrides/partials/nav.html
+++ /dev/null
@@ -1 +0,0 @@
-../../../../third_party/mkdocs-material/overrides/partials/nav.html
\ No newline at end of file