diff --git a/.github/dependabot.yml b/.github/dependabot.yml
deleted file mode 100644
index 973e39e..0000000
--- a/.github/dependabot.yml
+++ /dev/null
@@ -1,14 +0,0 @@
-version: 2
-updates:
-- package-ecosystem: gradle
-  directory: "/"
-  schedule:
-    interval: daily
-  open-pull-requests-limit: 10
-  ignore:
-  - dependency-name: com.google.errorprone:javac
-    versions:
-    - 1.8.0-u20
-  - dependency-name: org.checkerframework
-    versions:
-    - 0.5.18
diff --git a/.github/renovate.json b/.github/renovate.json
new file mode 100644
index 0000000..090f465
--- /dev/null
+++ b/.github/renovate.json
@@ -0,0 +1,11 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "config:base",
+    ":automergeAll",
+    ":automergeRequireAllStatusChecks",
+    "schedule:nonOfficeHours",
+    ":disableDependencyDashboard"
+  ],
+  "timezone": "America/Los_Angeles"
+}
diff --git a/.github/workflows/gradle.yml b/.github/workflows/gradle.yml
index a165171..2683a82 100644
--- a/.github/workflows/gradle.yml
+++ b/.github/workflows/gradle.yml
@@ -9,15 +9,18 @@ jobs:
 
     strategy:
       matrix:
-        java: [ '8', '11', '17', '19' ]
+        java: [ '11', '17', '21' ]
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Set up JDK
-      uses: actions/setup-java@v1
+      uses: actions/setup-java@v3
       with:
+        distribution: 'temurin'
         java-version: ${{ matrix.java }}
     - name: ./gradlew build javadoc
       run: ./gradlew build
     - name: ./gradlew requireJavadoc
       run: ./gradlew requireJavadoc
+    - name: ./gradlew spotlessCheck
+      run: ./gradlew spotlessCheck
diff --git a/.travis.yml b/.travis.yml
index fee1002..894df40 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,7 +11,7 @@ cache:
     - $HOME/.m2/
 
 jdk:
-  - oraclejdk8
+  - oraclejdk17
 
 # Add "verGJF" task when google-java-format handles type annotations better;
 # see https://github.com/google/google-java-format/issues/5
diff --git a/build.gradle b/build.gradle
index 7c41329..183414a 100644
--- a/build.gradle
+++ b/build.gradle
@@ -2,52 +2,51 @@ plugins {
   id 'java'
   id 'application'
 
-  // To create a fat jar build/libs/html-pretty-print-all.jar, run: ./gradlew shadowJar
-  id 'com.github.johnrengelman.shadow' version '7.1.2'
+  // To create a fat jar build/libs/...-all.jar, run: ./gradlew shadowJar
+  id 'com.github.johnrengelman.shadow' version '8.1.1'
 
   // Code formatting; defines targets "spotlessApply" and "spotlessCheck"
-  id "com.diffplug.spotless" version "6.12.0"
+  // Requires JDK 11 or higher; the plugin crashes under JDK 8.
+  id 'com.diffplug.spotless' version '6.22.0'
 
   // Error Prone linter
-  id("net.ltgt.errorprone") version "3.0.1"
+  id('net.ltgt.errorprone') version '3.1.0'
 
   // Checker Framework pluggable type-checking
-  id 'org.checkerframework' version '0.6.20'
+  id 'org.checkerframework' version '0.6.34'
 }
 
 repositories {
-    mavenCentral()
+  mavenCentral()
 }
 
 dependencies {
-    // This dependency is found on compile classpath of this component and consumers.
-    implementation 'com.google.guava:guava:31.1-jre'
+  implementation 'com.google.guava:guava:32.1.3-jre'
+  implementation 'org.ccil.cowan.tagsoup:tagsoup:1.2.1'
+  implementation 'xom:xom:1.3.9'
 
-    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.9.1'
-    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine'
-
-    // https://mvnrepository.com/artifact/org.ccil.cowan.tagsoup/tagsoup
-    implementation group: 'org.ccil.cowan.tagsoup', name: 'tagsoup', version: '1.2.1'
-
-    // https://mvnrepository.com/artifact/xom/xom
-    implementation group: 'xom', name: 'xom', version: '1.3.8'
+  testImplementation 'org.junit.jupiter:junit-jupiter-api:5.10.0'
+  testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine'
 }
 
 application {
   mainClass = 'org.plumelib.htmlprettyprint.HtmlPrettyPrint'
 }
 
+sourceCompatibility = 11
+targetCompatibility = 11
+
 test {
-    useJUnitPlatform {
-        includeEngines 'junit-jupiter'
-        excludeEngines 'junit-vintage'
-    }
+  useJUnitPlatform {
+    includeEngines 'junit-jupiter'
+    excludeEngines 'junit-vintage'
+  }
 }
 
 spotless {
   format 'misc', {
     // define the files to apply `misc` to
-    target '*.gradle', '*.md', '.gitignore'
+    target '*.md', '.gitignore'
 
     // define the steps to apply to those files
     trimTrailingWhitespace()
@@ -55,22 +54,29 @@ spotless {
     endWithNewline()
   }
   java {
-    targetExclude("**/WeakIdentityHashMap.java")
+    targetExclude('**/WeakIdentityHashMap.java')
     googleJavaFormat()
     formatAnnotations()
   }
+  groovyGradle {
+    target '**/*.gradle'
+    greclipse()  // which formatter Spotless should use to format .gradle files.
+    indentWithSpaces(2)
+    trimTrailingWhitespace()
+    // endWithNewline() // Don't want to end empty files with a newline
+  }
 }
 
 /// Error Prone linter
 
 dependencies {
-  errorprone("com.google.errorprone:error_prone_core:2.16")
+  errorprone('com.google.errorprone:error_prone_core:2.23.0')
 }
 tasks.withType(JavaCompile).configureEach {
-  options.compilerArgs << "-Xlint:all" << "-Werror"
+  // "-processing" avoids javac warning "No processor claimed any of these annotations".
+  options.compilerArgs << '-Xlint:all,-processing' << '-Werror'
   options.errorprone {
-    enabled = JavaVersion.current() != JavaVersion.VERSION_1_8
-    disable("ReferenceEquality") // Use Interning Checker instead.
+    disable('ReferenceEquality') // Use Interning Checker instead.
   }
 }
 
@@ -79,9 +85,9 @@ tasks.withType(JavaCompile).configureEach {
 apply plugin: 'org.checkerframework'
 
 dependencies {
-  compileOnly 'io.github.eisop:checker-qual:3.28.0-eisop1'
-  testCompileOnly 'io.github.eisop:checker-qual:3.28.0-eisop1'
-  checkerFramework 'io.github.eisop:checker:3.28.0-eisop1'
+  compileOnly 'io.github.eisop:checker-qual:3.34.0-eisop1'
+  testCompileOnly 'io.github.eisop:checker-qual:3.34.0-eisop1'
+  checkerFramework 'io.github.eisop:checker:3.34.0-eisop1'
 }
 
 checkerFramework {
@@ -103,18 +109,19 @@ checkerFramework {
     '-Werror',
     '-AcheckPurityAnnotations',
     '-ArequirePrefixInWarningSuppressions',
+    '-AwarnRedundantAnnotations',
     '-AwarnUnneededSuppressions',
     '-AnoJreVersionCheck',
   ]
 }
 
 // To use a locally-built Checker Framework, run gradle with "-PcfLocal".
-if (project.hasProperty("cfLocal")) {
-  def cfHome = String.valueOf(System.getenv("CHECKERFRAMEWORK"))
+if (project.hasProperty('cfLocal')) {
+  def cfHome = String.valueOf(System.getenv('CHECKERFRAMEWORK'))
   dependencies {
-    compileOnly files(cfHome + "/checker/dist/checker-qual.jar")
-    testCompileOnly files(cfHome + "/checker/dist/checker-qual.jar")
-    checkerFramework files(cfHome + "/checker/dist/checker.jar")
+    compileOnly files(cfHome + '/checker/dist/checker-qual.jar')
+    testCompileOnly files(cfHome + '/checker/dist/checker-qual.jar')
+    checkerFramework files(cfHome + '/checker/dist/checker.jar')
   }
 }
 
@@ -124,6 +131,13 @@ if (project.hasProperty("cfLocal")) {
 javadoc {
   options.addStringOption('Xwerror', '-Xdoclint:all')
   options.addStringOption('private', '-quiet')
+  options.addStringOption('source', '11')
+  doLast {
+    ant.replaceregexp(match:"@import url\\('resources/fonts/dejavu.css'\\);\\s*", replace:'',
+    flags:'g', byline:true) {
+      fileset(dir: destinationDir)
+    }
+  }
 }
 check.dependsOn javadoc
 
@@ -131,13 +145,13 @@ configurations {
   requireJavadoc
 }
 dependencies {
-  requireJavadoc "org.plumelib:require-javadoc:1.0.6"
+  requireJavadoc 'org.plumelib:require-javadoc:1.0.6'
 }
 task requireJavadoc(type: JavaExec) {
   description = 'Ensures that Javadoc documentation exists.'
-  mainClass = "org.plumelib.javadoc.RequireJavadoc"
+  mainClass = 'org.plumelib.javadoc.RequireJavadoc'
   classpath = configurations.requireJavadoc
-  args "src/main/java"
+  args 'src/main/java'
 }
 check.dependsOn requireJavadoc
 
@@ -145,6 +159,6 @@ check.dependsOn requireJavadoc
 
 /* Make Emacs TAGS table */
 task tags(type: Exec) {
-  description "Run etags to create an Emacs TAGS table"
-  commandLine "bash", "-c", "find src/ -name '*.java' | sort | xargs etags"
+  description 'Run etags to create an Emacs TAGS table'
+  commandLine 'bash', '-c', "find src/ -name '*.java' | sort | xargs etags"
 }
diff --git a/gradle/wrapper/gradle-wrapper.jar b/gradle/wrapper/gradle-wrapper.jar
index 943f0cb..7f93135 100644
Binary files a/gradle/wrapper/gradle-wrapper.jar and b/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index f398c33..3fa8f86 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -1,6 +1,7 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-7.6-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.4-bin.zip
 networkTimeout=10000
+validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
diff --git a/gradlew b/gradlew
index 65dcd68..1aa94a4 100755
--- a/gradlew
+++ b/gradlew
@@ -83,10 +83,8 @@ done
 # This is normally unused
 # shellcheck disable=SC2034
 APP_BASE_NAME=${0##*/}
-APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
-
-# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
-DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd "${APP_HOME:-./}" > /dev/null && pwd -P ) || exit
 
 # Use the maximum available, or set MAX_FD != -1 to use that value.
 MAX_FD=maximum
@@ -133,10 +131,13 @@ location of your Java installation."
     fi
 else
     JAVACMD=java
-    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
 
 Please set the JAVA_HOME variable in your environment to match the
 location of your Java installation."
+    fi
 fi
 
 # Increase the maximum file descriptors if we can.
@@ -144,7 +145,7 @@ if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
     case $MAX_FD in #(
       max*)
         # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
-        # shellcheck disable=SC3045 
+        # shellcheck disable=SC2039,SC3045
         MAX_FD=$( ulimit -H -n ) ||
             warn "Could not query maximum file descriptor limit"
     esac
@@ -152,7 +153,7 @@ if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
       '' | soft) :;; #(
       *)
         # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
-        # shellcheck disable=SC3045 
+        # shellcheck disable=SC2039,SC3045
         ulimit -n "$MAX_FD" ||
             warn "Could not set maximum file descriptor limit to $MAX_FD"
     esac
@@ -197,11 +198,15 @@ if "$cygwin" || "$msys" ; then
     done
 fi
 
-# Collect all arguments for the java command;
-#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
-#     shell script including quotes and variable substitutions, so put them in
-#     double quotes to make sure that they get re-expanded; and
-#   * put everything else in single quotes, so that it's not re-expanded.
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
 
 set -- \
         "-Dorg.gradle.appname=$APP_BASE_NAME" \
diff --git a/settings.gradle b/settings.gradle
index 48b88a4..fb7e53a 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -1,2 +1,8 @@
+buildscript {
+  if (JavaVersion.current() == JavaVersion.VERSION_1_8) {
+    throw new Error("Use Java 11 or later.")
+  }
+}
+
 // Project name is read-only in build scripts, and defaults to directory name.
 rootProject.name = 'html-pretty-print'