See weblog entry: https://eckig.github.io/blog/2014/11/06/resizable-grid-using-canvas/

ResizableGrid.java

public class ResizableGrid extends Pane {
   
   // This is to make the stroke be drawn 'on pixel'.
   private static final double HALF_PIXEL_OFFSET = -0.5;

   private final Canvas canvas = new Canvas();
   private boolean needsLayout = false;
   
   private final StyleableObjectProperty<Paint> gridColor = new StyleableObjectProperty<Paint>(
         Color.rgb(222, 248, 255)) {

      @Override
      public CssMetaData<? extends Styleable, Paint> getCssMetaData() {
         return StyleableProperties.GRID_COLOR;
      }

      @Override
      public Object getBean() {
         return ResizableGrid.this;
      }

      @Override
      public String getName() {
         return "gridColor";
      }

      @Override
      protected void invalidated() {
         needsLayout = true;
         requestLayout();
      }
   };
   
   private final StyleableObjectProperty<Number> gridSpacing = new StyleableObjectProperty<Number>(15) {

      @Override
      public CssMetaData<? extends Styleable, Number> getCssMetaData() {
         return StyleableProperties.GRID_SPACING;
      }

      @Override
      public Object getBean() {
         return ResizableGrid.this;
      }

      @Override
      public String getName() {
         return "gridSpacing";
      }

      @Override
      protected void invalidated() {
         needsLayout = true;
         requestLayout();
      }
   };

   public ResizableGrid() {
      getStyleClass().add("graph-grid");
      getChildren().add(canvas);
   }

   @Override
   protected void layoutChildren() {
      final int top = (int) snappedTopInset();
      final int right = (int) snappedRightInset();
      final int bottom = (int) snappedBottomInset();
      final int left = (int) snappedLeftInset();
      final int width = (int) getWidth() - left - right;
      final int height = (int) getHeight() - top - bottom;
      final double spacing = gridSpacing.get().doubleValue();
      
      canvas.setLayoutX(left);
      canvas.setLayoutY(top);
      
      if (width != canvas.getWidth() || height != canvas.getHeight() || needsLayout) {
         canvas.setWidth(width);
         canvas.setHeight(height);
         
         GraphicsContext g = canvas.getGraphicsContext2D();
         g.clearRect(0, 0, width, height);
         g.setFill(gridColor.get());

         final int hLineCount = (int) Math.floor((height + 1) / spacing);
         final int vLineCount = (int) Math.floor((width + 1) / spacing);

         for (int i = 0; i < hLineCount; i++) {
            g.strokeLine(0, snap((i + 1) * spacing), width, snap((i + 1) * spacing));
         }

         for (int i = 0; i < vLineCount; i++) {
            g.strokeLine(snap((i + 1) * spacing), 0, snap((i + 1) * spacing), height);
         }

         needsLayout = false;
      }
   }
   
   private static double snap(double y) {
      return ((int) y) + HALF_PIXEL_OFFSET;
   }

   /**
    * @return The CssMetaData associated with this class, including the
    *         CssMetaData of its super classes.
    */
   public static List<CssMetaData<? extends Styleable, ?>> getClassCssMetaData() {
      return StyleableProperties.STYLEABLES;
   }

   @Override
   public List<CssMetaData<? extends Styleable, ?>> getCssMetaData() {
      return getClassCssMetaData();
   }

   private static class StyleableProperties {

      private static final CssMetaData<ResizableGrid, Paint> GRID_COLOR = new CssMetaData<ResizableGrid, Paint>(
            "-graph-grid-color", PaintConverter.getInstance()) {

         @Override
         public boolean isSettable(ResizableGrid node) {
            return !node.gridColor.isBound();
         }

         @Override
         public StyleableProperty<Paint> getStyleableProperty(ResizableGrid node) {
            return node.gridColor;
         }
      };
      
      private static final CssMetaData<ResizableGrid, Number> GRID_SPACING = new CssMetaData<ResizableGrid, Number>(
            "-graph-grid-spacing", SizeConverter.getInstance()) {

         @Override
         public boolean isSettable(ResizableGrid node) {
            return !node.gridSpacing.isBound();
         }

         @Override
         public StyleableProperty<Number> getStyleableProperty(ResizableGrid node) {
            return node.gridSpacing;
         }
      };

      private static final List<CssMetaData<? extends Styleable, ?>> STYLEABLES;
      static {
         List<CssMetaData<? extends Styleable, ?>> styleables = new ArrayList<CssMetaData<? extends Styleable, ?>>(
               Pane.getClassCssMetaData());
         styleables.add(GRID_COLOR);
         styleables.add(GRID_SPACING);
         STYLEABLES = Collections.unmodifiableList(styleables);
      }
   }
}

Thanks Steffen - works like a charm.
I think there should be g.setStroke instead of g.setFill for g.strokeLine.