Update Javadoc theme

src/main/javadoc/theme.overlay.css

@@ -0,0 +1,36 @@
+/*
+  This stylesheet file makes the page appear dark.
+  Stolen from:
+  https://docs.oracle.com/en/java/javase/21/javadoc/programmers-guide-javadoc-css-themes.html
+ */
+:root {
+    --body-text-color: #e0e0e3;
+    --block-text-color: #e6e7ef;
+    --body-background-color: #404040;
+    --section-background-color: #484848;
+    --detail-background-color: #404040;
+    --navbar-background-color: #505076;
+    --navbar-text-color: #ffffff;
+    --subnav-background-color: #303030;
+    --selected-background-color: #f8981d;
+    --selected-text-color: #253441;
+    --selected-link-color: #1f389c;
+    --even-row-color: #484848;
+    --odd-row-color: #383838;
+    --title-color: #ffffff;
+    --link-color: #a0c0f8;
+    --link-color-active: #ffb863;
+    --snippet-background-color: #383838;
+    --snippet-text-color: var(--block-text-color);
+    --snippet-highlight-color: #f7c590;
+    --border-color: #383838;
+    --table-border-color: #000000;
+    --search-input-background-color: #000000;
+    --search-input-text-color: #ffffff;
+    --search-input-placeholder-color: #909090;
+    --search-tag-highlight-color: #ffff00;
+    --copy-icon-brightness: 250%;
+    --copy-button-background-color-active: rgba(168, 168, 176, 0.3);
+    --invalid-tag-background-color: #ffe6e6;
+    --invalid-tag-text-color: #000000;
+}

src/main/javadoc/theme.update.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+# This script's sole purpose is to combine
+# 'theme.source.css' and 'theme.overlay.css'
+# and create 'theme.css'.
+rm -rf theme.css
+cp theme.source.css theme.css
+cat theme.overlay.css >> theme.css