Created new SearchBox class with button to clear the search.

Source/Editor/GUI/Input/SearchBox.cs

@@ -0,0 +1,50 @@
+using FlaxEngine.GUI;
+
+namespace FlaxEditor.GUI.Input
+{
+    /// <summary>
+    /// Search box control which can gather text search input from the user.
+    /// </summary>
+    public class SearchBox : TextBox
+    {
+        /// <summary>
+        /// A button that clears the search bar.
+        /// </summary>
+        public Button ClearSearchButton { get; }
+        
+        /// <summary>
+        /// Init search box
+        /// </summary>
+        public SearchBox()
+        : this(false, 0, 0)
+        {
+        }
+        
+        /// <summary>
+        /// Init search box
+        /// </summary>
+        public SearchBox(bool isMultiline, float x, float y, float width = 120)
+        : base(isMultiline, x, y, width)
+        {
+            WatermarkText = "Search...";
+            
+            ClearSearchButton = new Button
+            {
+                Parent = this,
+                Width = 15.0f,
+                Height = 14.0f,
+                AnchorPreset = AnchorPresets.TopRight,
+                Text = "X",
+                TooltipText = "Cancel Search.",
+                BackgroundColor = Style.Current.TextBoxBackground,
+                BorderColor = Style.Current.TextBoxBackground,
+                Visible = false,
+            };
+            ClearSearchButton.LocalY += 2;
+            ClearSearchButton.LocalX -= 2;
+            ClearSearchButton.Clicked += Clear;
+
+            TextChanged += () => ClearSearchButton.Visible = !string.IsNullOrEmpty(Text);
+        }
+    }
+}

Source/Editor/Windows/ContentWindow.cs

@@ -113,10 +113,9 @@ namespace FlaxEditor.Windows
                 IsScrollable = false,
                 Offsets = new Margin(0, 0, 0, 18 + 6),
             };
-            _foldersSearchBox = new TextBox
+            _foldersSearchBox = new SearchBox
             {
                 AnchorPreset = AnchorPresets.HorizontalStretchMiddle,
-                WatermarkText = "Search...",
                 Parent = headerPanel,
                 Bounds = new Rectangle(4, 4, headerPanel.Width - 8, 18),
             };
@@ -149,7 +148,7 @@ namespace FlaxEditor.Windows
                 Parent = _split.Panel2,
             };
             const float viewDropdownWidth = 50.0f;
-            _itemsSearchBox = new TextBox
+            _itemsSearchBox = new SearchBox
             {
                 AnchorPreset = AnchorPresets.HorizontalStretchMiddle,
                 WatermarkText = "Search...",

Source/Editor/Windows/OutputLogWindow.cs

@@ -7,6 +7,7 @@ using System.Text;
 using System.Text.RegularExpressions;
 using System.Xml;
 using FlaxEditor.GUI.ContextMenu;
+using FlaxEditor.GUI.Input;
 using FlaxEditor.Options;
 using FlaxEngine;
 using FlaxEngine.GUI;
@@ -157,9 +158,8 @@ namespace FlaxEditor.Windows
                 Parent = this,
             };
             _viewDropdown.Clicked += OnViewButtonClicked;
-            _searchBox = new TextBox(false, _viewDropdown.Right + 2, 2, Width - _viewDropdown.Right - 2 - _scrollSize)
+            _searchBox = new SearchBox(false, _viewDropdown.Right + 2, 2, Width - _viewDropdown.Right - 2 - _scrollSize)
             {
-                WatermarkText = "Search...",
                 Parent = this,
             };
             _searchBox.TextChanged += Refresh;

Source/Editor/Windows/SceneTreeWindow.cs

@@ -6,6 +6,7 @@ using FlaxEditor.Gizmo;
 using FlaxEditor.Content;
 using FlaxEditor.GUI.Tree;
 using FlaxEditor.GUI.Drag;
+using FlaxEditor.GUI.Input;
 using FlaxEditor.SceneGraph;
 using FlaxEditor.SceneGraph.GUI;
 using FlaxEditor.Scripting;
@@ -49,10 +50,9 @@ namespace FlaxEditor.Windows
                 IsScrollable = false,
                 Offsets = new Margin(0, 0, 0, 18 + 6),
             };
-            _searchBox = new TextBox
+            _searchBox = new SearchBox
             {
                 AnchorPreset = AnchorPresets.HorizontalStretchMiddle,
-                WatermarkText = "Search...",
                 Parent = headerPanel,
                 Bounds = new Rectangle(4, 4, headerPanel.Width - 8, 18),
             };

Source/Editor/Windows/ToolboxWindow.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using FlaxEditor.GUI.Input;
 using FlaxEditor.GUI.Tabs;
 using FlaxEditor.GUI.Tree;
 using FlaxEditor.Scripting;
@@ -130,10 +131,9 @@ namespace FlaxEditor.Windows
             };
 
             _groupSearch = CreateGroupWithList(_actorGroups, "Search", 26);
-            _searchBox = new TextBox
+            _searchBox = new SearchBox
             {
                 AnchorPreset = AnchorPresets.HorizontalStretchTop,
-                WatermarkText = "Search...",
                 Parent = _groupSearch.Parent.Parent,
                 Bounds = new Rectangle(4, 4, _actorGroups.Width - 8, 18),
             };