Improve utility methods in Styles class

- Added more methods to manipulate style properties.
- Added unit tests.

base/src/main/java/atlantafx/base/theme/Styles.java

@@ -2,6 +2,9 @@
 
 package atlantafx.base.theme;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import java.util.Base64;
 import java.util.Objects;
 import javafx.css.PseudoClass;
 import javafx.scene.Node;
@@ -14,6 +17,8 @@ import javafx.scene.control.TabPane;
 @SuppressWarnings("unused")
 public final class Styles {
 
+    public static final String DATA_URI_PREFIX = "data:base64,";
+
     // Colors
 
     public static final String ACCENT = "accent";
@@ -92,6 +97,10 @@ public final class Styles {
     /**
      * Adds given style class to the node if it's not present, otherwise
      * removes it.
+     *
+     * @param node       the target node
+     * @param styleClass the style class to be toggled
+     * @throws NullPointerException if node or style class is null
      */
     public static void toggleStyleClass(Node node, String styleClass) {
         if (node == null) {
@@ -102,7 +111,7 @@ public final class Styles {
         }
 
         int idx = node.getStyleClass().indexOf(styleClass);
-        if (idx > 0) {
+        if (idx >= 0) {
             node.getStyleClass().remove(idx);
         } else {
             node.getStyleClass().add(styleClass);
@@ -113,6 +122,11 @@ public final class Styles {
      * Adds given style class to the node and removes the excluded classes.
      * This method is supposed to be used when only one from a set of classes
      * have to be present at once.
+     *
+     * @param node       the target node
+     * @param styleClass the style class to be toggled
+     * @param excludes   the style classes to be excluded
+     * @throws NullPointerException if node or styleClass is null
      */
     public static void addStyleClass(Node node, String styleClass, String... excludes) {
         if (node == null) {
@@ -125,13 +139,21 @@ public final class Styles {
         if (excludes != null && excludes.length > 0) {
             node.getStyleClass().removeAll(excludes);
         }
-        node.getStyleClass().add(styleClass);
+
+        if (!node.getStyleClass().contains(styleClass)) {
+            node.getStyleClass().add(styleClass);
+        }
     }
 
     /**
      * Activates given pseudo-class to the node and deactivates the excluded pseudo-classes.
      * This method is supposed to be used when only one from a set of pseudo-classes
      * have to be present at once.
+     *
+     * @param node        the node to activate the pseudo-class on
+     * @param pseudoClass the pseudo-class to be activated
+     * @param excludes    the pseudo-classes to be deactivated
+     * @throws NullPointerException if node or pseudo-class is null
      */
     public static void activatePseudoClass(Node node, PseudoClass pseudoClass, PseudoClass... excludes) {
         if (node == null) {
@@ -149,17 +171,88 @@ public final class Styles {
         node.pseudoClassStateChanged(pseudoClass, true);
     }
 
+    /**
+     * Appends CSS style declaration to the specified node.
+     * There's no check for duplicates, so the CSS declarations with the same property
+     * name can be appended multiple times.
+     *
+     * @param node  the node to append the new style declaration
+     * @param prop  CSS property name
+     * @param value CSS property value
+     * @throws NullPointerException if node is null
+     */
     public static void appendStyle(Node node, String prop, String value) {
+        if (node == null) {
+            throw new NullPointerException("Node cannot be null!");
+        }
+
         if (prop == null || prop.isBlank() || value == null || value.isBlank()) {
-            System.err.printf("Ignoring invalid style: property='%s', value='%s'%n", prop, value);
+            System.err.printf("Ignoring invalid style: property = '%s', value = '%s'%n", prop, value);
             return;
         }
 
         var style = Objects.requireNonNullElse(node.getStyle(), "");
-        if (!style.endsWith(";")) {
+        if (!style.isEmpty() && !style.endsWith(";")) {
             style += ";";
         }
         style = style + prop.trim() + ":" + value.trim() + ";";
         node.setStyle(style);
     }
+
+    /**
+     * Removes the specified CSS style declaration from the specified node.
+     *
+     * @param node the node to remove the style from
+     * @param prop the name of the style property to remove
+     * @throws NullPointerException if node is null
+     */
+    public static void removeStyle(Node node, String prop) {
+        if (node == null) {
+            throw new NullPointerException("Node cannot be null!");
+        }
+
+        var currentStyle = node.getStyle();
+        if (currentStyle == null || currentStyle.isBlank()) {
+            return;
+        }
+
+        if (prop == null || prop.isBlank()) {
+            System.err.printf("Ignoring invalid property = '%s'%n", prop);
+            return;
+        }
+
+        String[] stylePairs = currentStyle.split(";");
+        var newStyle = new StringBuilder();
+
+        for (var s : stylePairs) {
+            String[] styleParts = s.split(":");
+            if (!styleParts[0].trim().equals(prop)) {
+                newStyle.append(s);
+                newStyle.append(";");
+            }
+        }
+
+        node.setStyle(newStyle.toString());
+    }
+
+    /**
+     * Converts a CSS string to a Base64-encoded data URI. The resulting string is
+     * an inline data URI that can be applied to any node in the following manner:
+     *
+     * <pre>{@code}
+     * var dataUri = Styles.toDataURI();
+     * node.getStylesheets().add(dataUri);
+     * node.getStylesheets().contains(dataUri);
+     * node.getStylesheets().remove(dataUri);
+     * </pre>
+     *
+     * @param css the CSS string to encode
+     * @return the resulting data URI string
+     */
+    public static String toDataURI(String css) {
+        if (css == null) {
+            throw new NullPointerException("CSS string cannot be null!");
+        }
+        return DATA_URI_PREFIX + new String(Base64.getEncoder().encode(css.getBytes(UTF_8)), UTF_8);
+    }
 }

base/src/test/java/atlantafx/base/theme/StylesTest.java

@@ -0,0 +1,332 @@
+package atlantafx.base.theme;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatNullPointerException;
+
+import java.util.Base64;
+import javafx.css.PseudoClass;
+import javafx.scene.layout.Region;
+import org.junit.jupiter.api.Test;
+
+public class StylesTest {
+
+    PseudoClass pcFirst = PseudoClass.getPseudoClass("first");
+    PseudoClass pcSecond = PseudoClass.getPseudoClass("second");
+    PseudoClass pcExcluded = PseudoClass.getPseudoClass("excluded");
+
+    @Test
+    @SuppressWarnings("DataFlowIssue")
+    public void testToggleStyleClassNPE() {
+        assertThatNullPointerException().isThrownBy(
+            () -> Styles.toggleStyleClass(new Region(), null)
+        );
+        assertThatNullPointerException().isThrownBy(
+            () -> Styles.toggleStyleClass(null, "any")
+        );
+    }
+
+    @Test
+    public void testToggleStyleClassOn() {
+        var node = new Region();
+        node.getStyleClass().add("first");
+        assertThat(node.getStyleClass()).containsExactly("first");
+
+        Styles.toggleStyleClass(node, "second");
+        assertThat(node.getStyleClass()).containsExactly("first", "second");
+    }
+
+    @Test
+    public void testToggleStyleClassMultipleOn() {
+        var node = new Region();
+        node.getStyleClass().addAll("first", "second", "third");
+        assertThat(node.getStyleClass()).containsExactly("first", "second", "third");
+
+        Styles.toggleStyleClass(node, "fourth");
+        assertThat(node.getStyleClass()).containsExactly("first", "second", "third", "fourth");
+    }
+
+    @Test
+    public void testToggleStyleClassOff() {
+        var node = new Region();
+        node.getStyleClass().add("sole");
+        assertThat(node.getStyleClass()).containsExactly("sole");
+
+        Styles.toggleStyleClass(node, "sole");
+        assertThat(node.getStyleClass()).isEmpty();
+    }
+
+    @Test
+    public void testToggleStyleClassMultipleOff() {
+        var node = new Region();
+        node.getStyleClass().addAll("first", "second", "third");
+        assertThat(node.getStyleClass()).containsExactly("first", "second", "third");
+
+        Styles.toggleStyleClass(node, "second");
+        assertThat(node.getStyleClass()).containsExactly("first", "third");
+    }
+
+    ///////////////////////////////////////////////////////////////////////////
+
+    @Test
+    @SuppressWarnings("DataFlowIssue")
+    public void testAddStyleClassClassNPE() {
+        assertThatNullPointerException().isThrownBy(
+            () -> Styles.addStyleClass(new Region(), null)
+        );
+        assertThatNullPointerException().isThrownBy(
+            () -> Styles.addStyleClass(null, "any")
+        );
+    }
+
+    @Test
+    public void testAddStyleClassAdds() {
+        var node = new Region();
+        node.getStyleClass().addAll("first");
+        assertThat(node.getStyleClass()).containsExactly("first");
+
+        Styles.addStyleClass(node, "second");
+        assertThat(node.getStyleClass()).containsExactly("first", "second");
+    }
+
+    @Test
+    public void testAddStyleClassExcludes() {
+        var node = new Region();
+        node.getStyleClass().addAll("first", "excluded");
+        assertThat(node.getStyleClass()).containsExactly("first", "excluded");
+
+        Styles.addStyleClass(node, "second", "excluded");
+        assertThat(node.getStyleClass()).containsExactly("first", "second");
+    }
+
+    @Test
+    public void testAddStyleClassIgnoresDuplicate() {
+        var node = new Region();
+        node.getStyleClass().addAll("first", "second", "excluded");
+        assertThat(node.getStyleClass()).containsExactly("first", "second", "excluded");
+
+        Styles.addStyleClass(node, "second", "excluded");
+        assertThat(node.getStyleClass()).containsExactly("first", "second");
+    }
+
+    ///////////////////////////////////////////////////////////////////////////
+
+    @Test
+    @SuppressWarnings("DataFlowIssue")
+    public void testActivatePseudoClassNPE() {
+        assertThatNullPointerException().isThrownBy(
+            () -> Styles.activatePseudoClass(new Region(), null)
+        );
+        assertThatNullPointerException().isThrownBy(
+            () -> Styles.activatePseudoClass(null, pcFirst)
+        );
+    }
+
+    @Test
+    public void testActivatePseudoClassActivates() {
+        var node = new Region();
+        node.pseudoClassStateChanged(pcFirst, true);
+        assertThat(node.getPseudoClassStates()).containsExactly(pcFirst);
+
+        Styles.activatePseudoClass(node, pcSecond);
+        assertThat(node.getPseudoClassStates()).containsExactly(pcFirst, pcSecond);
+    }
+
+    @Test
+    public void testActivatePseudoClassExcludes() {
+        var node = new Region();
+        node.pseudoClassStateChanged(pcFirst, true);
+        node.pseudoClassStateChanged(pcExcluded, true);
+        assertThat(node.getPseudoClassStates()).containsExactly(pcFirst, pcExcluded);
+
+        Styles.activatePseudoClass(node, pcSecond, pcExcluded);
+        assertThat(node.getPseudoClassStates()).containsExactly(pcFirst, pcSecond);
+    }
+
+    @Test
+    public void testActivatePseudoClassIgnoresDuplicate() {
+        var node = new Region();
+        node.pseudoClassStateChanged(pcFirst, true);
+        node.pseudoClassStateChanged(pcSecond, true);
+        node.pseudoClassStateChanged(pcExcluded, true);
+        assertThat(node.getPseudoClassStates()).containsExactly(pcFirst, pcSecond, pcExcluded);
+
+        Styles.activatePseudoClass(node, pcSecond, pcExcluded);
+        assertThat(node.getPseudoClassStates()).containsExactly(pcFirst, pcSecond);
+    }
+
+    ///////////////////////////////////////////////////////////////////////////
+
+    @Test
+    @SuppressWarnings("DataFlowIssue")
+    void testAppendStyleNullNode() {
+        assertThatNullPointerException().isThrownBy(
+            () -> Styles.appendStyle(null, "-fx-background-color", "red")
+        );
+    }
+
+    @Test
+    void testAppendStyleValid() {
+        var node = new Region();
+        Styles.appendStyle(node, "-fx-background-color", "red");
+        assertThat(node.getStyle()).isEqualTo("-fx-background-color:red;");
+    }
+
+    @Test
+    void testAppendStyleEmptyProperty() {
+        var node = new Region();
+        Styles.appendStyle(node, "", "red");
+        assertThat(node.getStyle()).isEmpty();
+    }
+
+    @Test
+    void testAppendStyleEmptyValue() {
+        var node = new Region();
+        Styles.appendStyle(node, "-fx-background-color", "");
+        assertThat(node.getStyle()).isEmpty();
+    }
+
+    @Test
+    void testAppendStyleNullProperty() {
+        var node = new Region();
+        Styles.appendStyle(node, null, "red");
+        assertThat(node.getStyle()).isEmpty();
+    }
+
+    @Test
+    void testAppendStyleNullValue() {
+        var node = new Region();
+        Styles.appendStyle(node, "-fx-background-color", null);
+        assertThat(node.getStyle()).isEmpty();
+    }
+
+    @Test
+    void testAppendStyleMultipleProperties() {
+        var node = new Region();
+        Styles.appendStyle(node, "-fx-background-color", "red");
+        Styles.appendStyle(node, "-fx-text-fill", "white");
+        assertThat(node.getStyle()).isEqualTo("-fx-background-color:red;-fx-text-fill:white;");
+    }
+
+    @Test
+    void testAppendStyleDuplicateProperty() {
+        var node = new Region();
+        Styles.appendStyle(node, "-fx-background-color", "red");
+        Styles.appendStyle(node, "-fx-background-color", "blue");
+        // that's it, "append" appends, no check for duplicates
+        assertThat(node.getStyle()).isEqualTo("-fx-background-color:red;-fx-background-color:blue;");
+    }
+
+    ///////////////////////////////////////////////////////////////////////////
+
+    @Test
+    void testRemoveStyleValidProperty() {
+        var node = new Region();
+        node.setStyle("-fx-background-color:red;-fx-text-fill:white;");
+        Styles.removeStyle(node, "-fx-background-color");
+        assertThat(node.getStyle())
+            .contains("-fx-text-fill:white;")
+            .doesNotContain("-fx-background-color:red;");
+    }
+
+    @Test
+    void testRemoveStyleNonexistentProperty() {
+        var node = new Region();
+        node.setStyle("-fx-background-color:red;");
+        Styles.removeStyle(node, "-fx-text-fill");
+        assertThat(node.getStyle()).contains("-fx-background-color:red;");
+    }
+
+    @Test
+    void testRemoveStyleNullProperty() {
+        var node = new Region();
+        node.setStyle("-fx-background-color:red;");
+        Styles.removeStyle(node, null);
+        assertThat(node.getStyle()).contains("-fx-background-color:red;");
+    }
+
+    @Test
+    void testRemoveStyleEmptyProperty() {
+        var node = new Region();
+        node.setStyle("-fx-background-color:red;");
+        Styles.removeStyle(node, "");
+        assertThat(node.getStyle()).contains("-fx-background-color:red;");
+    }
+
+    @Test
+    @SuppressWarnings("DataFlowIssue")
+    void testRemoveStyleNullNode() {
+        assertThatNullPointerException().isThrownBy(
+            () -> Styles.removeStyle(null, "-fx-background-color")
+        );
+    }
+
+    @Test
+    void testRemoveStyleFromEmptyNode() {
+        var node = new Region();
+        Styles.removeStyle(node, "-fx-background-color");
+        assertThat(node.getStyle()).isEmpty();
+    }
+
+    @Test
+    void testRemoveMultipleStyles() {
+        var node = new Region();
+        node.setStyle("-fx-background-color:red;-fx-text-fill:white;");
+        Styles.removeStyle(node, "-fx-background-color");
+        Styles.removeStyle(node, "-fx-text-fill");
+        assertThat(node.getStyle()).isEmpty();
+    }
+
+    ///////////////////////////////////////////////////////////////////////////
+
+    @Test
+    void testToDataURIWithValidCSS() {
+        String css = "body { font-size: 16px; }";
+
+        String dataUri = Styles.toDataURI(css);
+        byte[] decodedBytes = Base64.getDecoder().decode(dataUri.substring(dataUri.indexOf(",") + 1));
+
+        assertThat(dataUri).startsWith(Styles.DATA_URI_PREFIX);
+        assertThat(new String(decodedBytes)).isEqualTo(css);
+    }
+
+    @Test
+    void testToDataURIWithEmptyCSS() {
+        String css = "";
+
+        String dataUri = Styles.toDataURI(css);
+        byte[] decodedBytes = Base64.getDecoder().decode(dataUri.substring(dataUri.indexOf(",") + 1));
+
+        assertThat(dataUri).startsWith(Styles.DATA_URI_PREFIX);
+        assertThat(new String(decodedBytes)).isEmpty();
+    }
+
+    @Test
+    @SuppressWarnings("DataFlowIssue")
+    void testToDataURIWithNullCSS() {
+        assertThatNullPointerException().isThrownBy(
+            () -> Styles.toDataURI(null)
+        );
+    }
+
+    @Test
+    void testToDataURIWithWhitespaceCSS() {
+        String css = "   ";
+
+        String dataUri = Styles.toDataURI(css);
+        byte[] decodedBytes = Base64.getDecoder().decode(dataUri.substring(dataUri.indexOf(",") + 1));
+
+        assertThat(dataUri).startsWith(Styles.DATA_URI_PREFIX);
+        assertThat(new String(decodedBytes)).isEqualTo(css);
+    }
+
+    @Test
+    void testToDataURIWithSpecialCharactersCSS() {
+        String css = "#id { background-image: url('https://example.com/bg.png'); }";
+
+        String dataUri = Styles.toDataURI(css);
+        byte[] decodedBytes = Base64.getDecoder().decode(dataUri.substring(dataUri.indexOf(",") + 1));
+
+        assertThat(dataUri).startsWith(Styles.DATA_URI_PREFIX);
+        assertThat(new String(decodedBytes)).isEqualTo(css);
+    }
+}

sampler/src/main/java/atlantafx/sampler/page/components/ButtonPage.java

@@ -7,7 +7,6 @@ import atlantafx.base.util.BBCodeParser;
 import atlantafx.sampler.page.ExampleBox;
 import atlantafx.sampler.page.OutlinePage;
 import atlantafx.sampler.page.Snippet;
-import atlantafx.sampler.theme.CSSFragment;
 import javafx.geometry.Pos;
 import javafx.scene.control.Button;
 import javafx.scene.control.ContentDisplay;
@@ -395,7 +394,7 @@ public final class ButtonPage extends OutlinePage {
         //     -fx-font-size:  32px;
         //     -fx-icon-size:  32px;
         // }
-        new CSSFragment(dataClass).addTo(iconBtn);
+        iconBtn.getStylesheets().add(Styles.toDataURI(dataClass));
         //snippet_8:end
 
         var box = new HBox(HGAP_20, btn, iconBtn);

sampler/src/main/java/atlantafx/sampler/page/components/CalendarPage.java

@@ -8,7 +8,6 @@ import atlantafx.base.util.BBCodeParser;
 import atlantafx.sampler.page.ExampleBox;
 import atlantafx.sampler.page.OutlinePage;
 import atlantafx.sampler.page.Snippet;
-import atlantafx.sampler.theme.CSSFragment;
 import java.net.URI;
 import java.time.LocalDate;
 import java.time.LocalTime;
@@ -148,7 +147,7 @@ public final class CalendarPage extends OutlinePage {
     }
 
     private ExampleBox styleExample() {
-        var style = """
+        var dataClass = """
             .date-picker-popup {
                 -color-date-border: -color-accent-emphasis;
                 -color-date-month-year-bg: -color-accent-emphasis;
@@ -161,7 +160,7 @@ public final class CalendarPage extends OutlinePage {
         // -color-date-border: -color-accent-emphasis;
         // -color-date-month-year-bg: -color-accent-emphasis;
         // -color-date-month-year-fg: -color-fg-emphasis;
-        new CSSFragment(style).addTo(dp);
+        dp.getStylesheets().add(Styles.toDataURI(dataClass));
         //snippet_4:end
 
         var box = new HBox(dp);

sampler/src/main/java/atlantafx/sampler/page/components/PopoverPage.java

@@ -5,11 +5,11 @@ package atlantafx.sampler.page.components;
 import atlantafx.base.controls.InlineDatePicker;
 import atlantafx.base.controls.Popover;
 import atlantafx.base.controls.Popover.ArrowLocation;
+import atlantafx.base.theme.Styles;
 import atlantafx.base.util.BBCodeParser;
 import atlantafx.sampler.page.ExampleBox;
 import atlantafx.sampler.page.OutlinePage;
 import atlantafx.sampler.page.Snippet;
-import atlantafx.sampler.theme.CSSFragment;
 import java.net.URI;
 import java.time.LocalDate;
 import java.time.ZoneId;
@@ -51,7 +51,7 @@ public final class PopoverPage extends OutlinePage {
     }
 
     private ExampleBox usageExample() {
-        var datePickerStyle = """
+        var dataClass = """
             .popover .date-picker-popup {
               -color-date-border: transparent;
               -color-date-bg: transparent;
@@ -84,7 +84,7 @@ public final class PopoverPage extends OutlinePage {
         // -color-date-day-bg: transparent;
         // -color-date-month-year-bg: transparent;
         // -color-date-day-bg-hover: -color-bg-subtle;
-        new CSSFragment(datePickerStyle).addTo(datePicker);
+        datePicker.getStylesheets().add(Styles.toDataURI(dataClass));
 
         var pop2 = new Popover(datePicker);
         pop2.setHeaderAlwaysVisible(false);

sampler/src/main/java/atlantafx/sampler/page/components/ProgressIndicatorPage.java

@@ -8,7 +8,6 @@ import atlantafx.base.util.BBCodeParser;
 import atlantafx.sampler.page.ExampleBox;
 import atlantafx.sampler.page.OutlinePage;
 import atlantafx.sampler.page.Snippet;
-import atlantafx.sampler.theme.CSSFragment;
 import javafx.beans.binding.Bindings;
 import javafx.concurrent.Task;
 import javafx.geometry.HPos;
@@ -316,7 +315,7 @@ public final class ProgressIndicatorPage extends OutlinePage {
         // .example:danger  .label {
         //     -fx-text-fill: -color-fg-emphasis;
         // }
-        new CSSFragment(dataClass).addTo(content);
+        content.getStylesheets().add(Styles.toDataURI(dataClass));
 
         bar.progressProperty().addListener((obs, old, val) -> {
             if (val == null) {

sampler/src/main/java/atlantafx/sampler/page/general/IconsPage.java

@@ -8,7 +8,6 @@ import atlantafx.base.util.BBCodeParser;
 import atlantafx.sampler.page.ExampleBox;
 import atlantafx.sampler.page.OutlinePage;
 import atlantafx.sampler.page.Snippet;
-import atlantafx.sampler.theme.CSSFragment;
 import java.net.URI;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -80,7 +79,7 @@ public final class IconsPage extends OutlinePage {
     }
 
     private ExampleBox stackingExample() {
-        var style1 = """
+        var dataClass1 = """
             .stacked-ikonli-font-icon > .outer-icon {
                 -fx-icon-size: 48px;
                 -fx-icon-color: -color-danger-emphasis;
@@ -90,7 +89,7 @@ public final class IconsPage extends OutlinePage {
             }
             """;
 
-        var style2 = """
+        var dataClass2 = """
             .stacked-ikonli-font-icon > .outer-icon {
                 -fx-icon-size: 48px;
             }
@@ -115,7 +114,7 @@ public final class IconsPage extends OutlinePage {
         // .stacked-ikonli-font-icon > .inner-icon {
         //   -fx-icon-size: 24px;
         // }
-        new CSSFragment(style1).addTo(stackIcon1);
+        stackIcon1.getStylesheets().add(Styles.toDataURI(dataClass1));
 
         var outerIcon2 = new FontIcon(
             Material2OutlinedAL.CHECK_BOX_OUTLINE_BLANK
@@ -133,7 +132,7 @@ public final class IconsPage extends OutlinePage {
         // .stacked-ikonli-font-icon > .inner-icon {
         //   -fx-icon-size: 24px;
         // }
-        new CSSFragment(style2).addTo(stackIcon2);
+        stackIcon2.getStylesheets().add(Styles.toDataURI(dataClass2));
         //snippet_2:end
 
         var box = new HBox(HGAP_20, stackIcon1, stackIcon2);

sampler/src/main/java/atlantafx/sampler/theme/CSSFragment.java

@@ -1,61 +0,0 @@
-/* SPDX-License-Identifier: MIT */
-
-package atlantafx.sampler.theme;
-
-import static java.nio.charset.StandardCharsets.UTF_8;
-
-import java.util.Base64;
-import java.util.Objects;
-import javafx.scene.layout.Region;
-
-public final class CSSFragment {
-
-    private static final String DATA_URI_PREFIX = "data:base64,";
-
-    private final String css;
-
-    public CSSFragment(String css) {
-        this.css = Objects.requireNonNull(css);
-    }
-
-    public void addTo(Region region) {
-        Objects.requireNonNull(region);
-        region.getStylesheets().add(toDataURI());
-    }
-
-    public void removeFrom(Region region) {
-        Objects.requireNonNull(region);
-        region.getStylesheets().remove(toDataURI());
-    }
-
-    public boolean existsIn(Region region) {
-        Objects.requireNonNull(region);
-        return region.getStylesheets().contains(toDataURI());
-    }
-
-    @Override
-    public boolean equals(Object o) {
-        if (this == o) {
-            return true;
-        }
-        if (o == null || getClass() != o.getClass()) {
-            return false;
-        }
-        CSSFragment cssFragment = (CSSFragment) o;
-        return css.equals(cssFragment.css);
-    }
-
-    @Override
-    public int hashCode() {
-        return Objects.hash(css);
-    }
-
-    @Override
-    public String toString() {
-        return css;
-    }
-
-    public String toDataURI() {
-        return DATA_URI_PREFIX + new String(Base64.getEncoder().encode(css.getBytes(UTF_8)), UTF_8);
-    }
-}