diff --git a/sources/application/UI/Base/Component/Button/Button.php b/sources/application/UI/Base/Component/Button/Button.php
index 29cfcfe16..b5b1f815a 100644
--- a/sources/application/UI/Base/Component/Button/Button.php
+++ b/sources/application/UI/Base/Component/Button/Button.php
@@ -94,8 +94,6 @@ class Button extends UIBlock
 	protected $sJsCode;
 	/** @var string $sOnClickJsCode */
 	protected $sOnClickJsCode;
-	/** @var array */
-	protected $aAdditionalCSSClasses;
 
 	/**
 	 * Button constructor.
@@ -131,7 +129,6 @@ class Button extends UIBlock
 		$this->sJsCode = $sJsCode;
 		$this->sOnClickJsCode = $sOnClickJsCode;
 		$this->bIsDisabled = false;
-		$this->aAdditionalCSSClasses = [];
 		$this->aDataAttributes = ['role' => 'ibo-button'];
 	}
 
@@ -346,24 +343,4 @@ class Button extends UIBlock
 
 		return $this;
 	}
-
-	/**
-	 * @return string
-	 */
-	public function GetAdditionalCSSClass(): string
-	{
-		return implode(' ', $this->aAdditionalCSSClasses);
-	}
-
-	public function AddCSSClasses(string $sCSSClasses): self
-	{
-		foreach (explode(' ', $sCSSClasses) as $sCSSClass) {
-			if (!empty($sCSSClass)) {
-				$this->aAdditionalCSSClasses[$sCSSClass] = $sCSSClass;
-			}
-		}
-		return $this;
-	}
-
-
 }
\ No newline at end of file
diff --git a/sources/application/UI/Base/Component/DataTable/StaticTable/FormTable/FormTable.php b/sources/application/UI/Base/Component/DataTable/StaticTable/FormTable/FormTable.php
index 0509f29bd..a6a0c0863 100644
--- a/sources/application/UI/Base/Component/DataTable/StaticTable/FormTable/FormTable.php
+++ b/sources/application/UI/Base/Component/DataTable/StaticTable/FormTable/FormTable.php
@@ -29,9 +29,9 @@ class FormTable extends StaticTable
 	/** @var iUIBlock[] */
 	private $aRows;
 
-	public function __construct(string $sRef, string $sContainerCSSClass = '')
+	public function __construct(string $sRef, string $sContainerCSSClasses = '')
 	{
-		parent::__construct($sRef, $sContainerCSSClass);
+		parent::__construct($sRef, $sContainerCSSClasses);
 		$this->SetRef($sRef);
 		$this->aRows = [];
 	}
diff --git a/sources/application/UI/Base/Component/DataTable/StaticTable/StaticTable.php b/sources/application/UI/Base/Component/DataTable/StaticTable/StaticTable.php
index fe1b2c4ec..9feb1d5f3 100644
--- a/sources/application/UI/Base/Component/DataTable/StaticTable/StaticTable.php
+++ b/sources/application/UI/Base/Component/DataTable/StaticTable/StaticTable.php
@@ -51,10 +51,10 @@ class StaticTable extends UIContentBlock
 	 * ]
 	 */
 	private $aData;
-	
-	public function __construct(string $sId = null, string $sContainerCSSClass = '')
+
+	public function __construct(string $sId = null, string $sContainerCSSClasses = '')
 	{
-		parent::__construct($sId, $sContainerCSSClass);
+		parent::__construct($sId, $sContainerCSSClasses);
 		$this->aColumns = [];
 		$this->aData = [];
 	}
diff --git a/sources/application/UI/Base/Component/FieldBadge/FieldBadge.php b/sources/application/UI/Base/Component/FieldBadge/FieldBadge.php
index 72154a620..6813f50f5 100644
--- a/sources/application/UI/Base/Component/FieldBadge/FieldBadge.php
+++ b/sources/application/UI/Base/Component/FieldBadge/FieldBadge.php
@@ -19,8 +19,8 @@ class FieldBadge extends UIContentBlock
 	// Overloaded constants
 	public const BLOCK_CODE = 'ibo-field-badge';
 
-	public function __construct(string $sId = null, string $sContainerClass = '')
+	public function __construct(string $sId = null, string $sContainerClasses = '')
 	{
-		parent::__construct($sId, $sContainerClass);
+		parent::__construct($sId, $sContainerClasses);
 	}
 }
\ No newline at end of file
diff --git a/sources/application/UI/Base/Component/PopoverMenu/PopoverMenuItem/PopoverMenuItem.php b/sources/application/UI/Base/Component/PopoverMenu/PopoverMenuItem/PopoverMenuItem.php
index 56a316c96..765ac30cd 100644
--- a/sources/application/UI/Base/Component/PopoverMenu/PopoverMenuItem/PopoverMenuItem.php
+++ b/sources/application/UI/Base/Component/PopoverMenu/PopoverMenuItem/PopoverMenuItem.php
@@ -69,13 +69,13 @@ class PopoverMenuItem extends UIBlock
 	}
 
 	/**
-	 * @see \ApplicationPopupMenuItem::SetCssClasses()
-	 *
 	 * @param array $aCssClasses
 	 *
 	 * @return $this
+	 * @uses oPopupMenuItem
+	 * @uses \ApplicationPopupMenuItem::SetCssClasses()
 	 */
-	public function SetCssClasses(array $aCssClasses)
+	public function SetMenuItemCssClasses(array $aCssClasses)
 	{
 		$this->oPopupMenuItem->SetCssClasses($aCssClasses);
 
@@ -83,13 +83,13 @@ class PopoverMenuItem extends UIBlock
 	}
 
 	/**
-	 * @see \ApplicationPopupMenuItem::AddCssClass()
-	 *
 	 * @param string $sCssClass
 	 *
 	 * @return $this
+	 * @uses oPopupMenuItem
+	 * @uses \ApplicationPopupMenuItem::AddCssClass()
 	 */
-	public function AddCssClass(string $sCssClass)
+	public function AddMenuItemCssClass(string $sCssClass)
 	{
 		$this->oPopupMenuItem->AddCssClass($sCssClass);
 
@@ -97,10 +97,11 @@ class PopoverMenuItem extends UIBlock
 	}
 
 	/**
-	 * @see \ApplicationPopupMenuItem::GetCssClasses()
 	 * @return array
+	 * @uses oPopupMenuItem
+	 * @uses \ApplicationPopupMenuItem::GetCssClasses()
 	 */
-	public function GetCssClasses()
+	public function GetMenuItemCssClasses(): array
 	{
 		return $this->oPopupMenuItem->GetCssClasses();
 	}
diff --git a/sources/application/UI/Base/Layout/UIContentBlock.php b/sources/application/UI/Base/Layout/UIContentBlock.php
index 9238e0f05..84fc37623 100644
--- a/sources/application/UI/Base/Layout/UIContentBlock.php
+++ b/sources/application/UI/Base/Layout/UIContentBlock.php
@@ -28,8 +28,6 @@ class UIContentBlock extends UIBlock implements iUIContentBlock
 	public const BLOCK_CODE = 'ibo-content-block';
 	public const DEFAULT_HTML_TEMPLATE_REL_PATH = 'base/layouts/content-block/layout';
 
-	/** @var array */
-	protected $aCSSClasses;
 	/** @var array */
 	protected $aSubBlocks;
 	/** @var array */
@@ -40,15 +38,15 @@ class UIContentBlock extends UIBlock implements iUIContentBlock
 	 * Generates a <div> only if $sContainerClass if not empty or block has data attributes
 	 *
 	 * @param string|null $sId
-	 * @param string $sContainerClass
+	 * @param string $sContainerClasses list of additional CSS classes, space as separator
 	 */
-	public function __construct(string $sId = null, string $sContainerClass = '')
+	public function __construct(string $sId = null, string $sContainerClasses = '')
 	{
 		parent::__construct($sId);
 
 		$this->aSubBlocks = [];
 		$this->aDeferredBlocks = [];
-		$this->SetCSSClasses($sContainerClass);
+		$this->SetCSSClasses($sContainerClasses);
 	}
 
 	/**
@@ -121,43 +119,6 @@ class UIContentBlock extends UIBlock implements iUIContentBlock
 		return $this;
 	}
 
-	/**
-	 * @return string
-	 */
-	public function GetCSSClasses(): string
-	{
-		return implode(' ', $this->aCSSClasses);
-	}
-
-	/**
-	 * @param string $sCSSClasses
-	 *
-	 * @return UIContentBlock
-	 */
-	public function SetCSSClasses(string $sCSSClasses)
-	{
-		$this->aCSSClasses = [];
-		$this->AddCSSClasses($sCSSClasses);
-
-		return $this;
-	}
-
-	/**
-	 * @param string $sCSSClasses
-	 *
-	 * @return $this
-	 */
-	public function AddCSSClasses(string $sCSSClasses)
-	{
-		foreach (explode(' ', $sCSSClasses) as $sCSSClass) {
-			if (!empty($sCSSClass)) {
-				$this->aCSSClasses[$sCSSClass] = $sCSSClass;
-			}
-		}
-
-		return $this;
-	}
-
 	/**
 	 * @inheritDoc
 	 */
diff --git a/sources/application/UI/Base/UIBlock.php b/sources/application/UI/Base/UIBlock.php
index fdc845460..b68f4c1f5 100644
--- a/sources/application/UI/Base/UIBlock.php
+++ b/sources/application/UI/Base/UIBlock.php
@@ -83,9 +83,11 @@ abstract class UIBlock implements iUIBlock
 	/** @var array */
 	protected $aCssFilesRelPath;
 	/** @var array Array <KEY> => <VALUE> which will be output as HTML data-xxx attributes (eg. data-<KEY>="<VALUE>") */
-	protected $aDataAttributes;
+	protected $aDataAttributes = [];
 	/** @var bool show or hide the current block */
 	protected $bIsHidden;
+	/** @var array */
+	protected $aAdditionalCSSClasses = [];
 
 	/**
 	 * UIBlock constructor.
@@ -103,7 +105,6 @@ abstract class UIBlock implements iUIBlock
 		$this->aJsTemplateRelPath[self::ENUM_JS_TYPE_ON_READY] = static::DEFAULT_JS_ON_READY_TEMPLATE_REL_PATH;
 		$this->sCssTemplateRelPath = static::DEFAULT_CSS_TEMPLATE_REL_PATH;
 		$this->sGlobalTemplateRelPath = static::DEFAULT_GLOBAL_TEMPLATE_REL_PATH;
-		$this->aDataAttributes = [];
 		$this->bIsHidden = static::DEFAULT_IS_HIDDEN;
 	}
 
@@ -129,6 +130,7 @@ abstract class UIBlock implements iUIBlock
 		if (!in_array($sType, [self::ENUM_JS_TYPE_LIVE, self::ENUM_JS_TYPE_ON_INIT, self::ENUM_JS_TYPE_ON_READY])) {
 			throw new UIException($this, "Type of javascript $sType not supported");
 		}
+
 		return $this->aJsTemplateRelPath[$sType];
 	}
 
@@ -243,6 +245,7 @@ abstract class UIBlock implements iUIBlock
 	public function AddJsFileRelPath(string $sPath)
 	{
 		$this->aJsFilesRelPath[] = $sPath;
+
 		return $this;
 	}
 
@@ -252,6 +255,7 @@ abstract class UIBlock implements iUIBlock
 	public function AddCssFileRelPath(string $sPath)
 	{
 		$this->aCssFilesRelPath[] = $sPath;
+
 		return $this;
 	}
 
@@ -299,6 +303,49 @@ abstract class UIBlock implements iUIBlock
 		return $aFiles;
 	}
 
+	/**
+	 * @param string $sCSSClasses with space as separator, like <code>ibo-is-hidden ibo-alert--body</code>
+	 *
+	 * @return $this
+	 *
+	 * @use aAdditionalCSSClasses
+	 */
+	public function AddCSSClasses(string $sCSSClasses)
+	{
+		foreach (explode(' ', $sCSSClasses) as $sCSSClass) {
+			if (!empty($sCSSClass)) {
+				$this->aAdditionalCSSClasses[$sCSSClass] = $sCSSClass;
+			}
+		}
+
+		return $this;
+	}
+
+	/**
+	 * Overrides additional classes with the specified value
+	 *
+	 * @param string $sCSSClasses with space as separator, like <code>ibo-is-hidden ibo-alert--body</code>
+	 *
+	 * @return $this
+	 *
+	 * @use aAdditionalCSSClasses
+	 */
+	public function SetCSSClasses(string $sCSSClasses)
+	{
+		$this->aAdditionalCSSClasses = [];
+		$this->AddCSSClasses($sCSSClasses);
+
+		return $this;
+	}
+
+	/**
+	 * @return string
+	 */
+	public function GetAdditionalCSSClasses(): string
+	{
+		return implode(' ', $this->aAdditionalCSSClasses);
+	}
+
 	/**
 	 * Return an array of the URL of the block $sFilesType and its sub blocks.
 	 * URL is relative unless the $bAbsoluteUrl is set to true.
@@ -343,6 +390,7 @@ abstract class UIBlock implements iUIBlock
 	public function SetDataAttributes(array $aDataAttributes)
 	{
 		$this->aDataAttributes = $aDataAttributes;
+
 		return $this;
 	}
 
@@ -356,6 +404,7 @@ abstract class UIBlock implements iUIBlock
 	public function AddDataAttribute(string $sName, string $sValue)
 	{
 		$this->aDataAttributes[$sName] = $sValue;
+
 		return $this;
 	}
 
@@ -375,6 +424,7 @@ abstract class UIBlock implements iUIBlock
 	public function SetIsHidden(bool $bIsHidden)
 	{
 		$this->bIsHidden = $bIsHidden;
+
 		return $this;
 	}
 }
diff --git a/templates/base/components/alert/layout.html.twig b/templates/base/components/alert/layout.html.twig
index 4784fe226..d67d3a224 100644
--- a/templates/base/components/alert/layout.html.twig
+++ b/templates/base/components/alert/layout.html.twig
@@ -1,5 +1,5 @@
 <div id="{{ oUIBlock.GetId() }}"
-	 class="ibo-alert ibo-is-{{ oUIBlock.GetColor() }}{% if oUIBlock.IsOpenedByDefault() %} ibo-is-opened{% endif %}{% if oUIBlock.IsHidden() %} ibo-is-hidden{% endif %}">
+	 class="ibo-alert ibo-is-{{ oUIBlock.GetColor() }}{% if oUIBlock.IsOpenedByDefault() %} ibo-is-opened{% endif %}{% if oUIBlock.IsHidden() %} ibo-is-hidden{% endif %} {{ oUIBlock.GetAdditionalCSSClasses() }}">
 	{% if oUIBlock.IsCollapsible() %}
 		<div class="ibo-alert--action-button ibo-alert--maximize-button" data-role="ibo-alert--collapse-toggler">
 			<i class="fas fa-caret-down"></i>
diff --git a/templates/base/components/button/layout.html.twig b/templates/base/components/button/layout.html.twig
index 153dcb56c..856c334f6 100644
--- a/templates/base/components/button/layout.html.twig
+++ b/templates/base/components/button/layout.html.twig
@@ -1,5 +1,5 @@
 <button id="{{ oUIBlock.GetId() }}"
-        class="ibo-button ibo-is-{{ oUIBlock.GetActionType() }} ibo-is-{{ oUIBlock.GetColor() }} {{ oUIBlock.GetAdditionalCSSClass() }}{% if oUIBlock.IsHidden() %} ibo-is-hidden{% endif %}"
+        class="ibo-button ibo-is-{{ oUIBlock.GetActionType() }} ibo-is-{{ oUIBlock.GetColor() }} {{ oUIBlock.GetAdditionalCSSClasses() }}{% if oUIBlock.IsHidden() %} ibo-is-hidden{% endif %}"
         {% if oUIBlock.GetDataAttributes() %}
                 {% for sName, sValue in oUIBlock.GetDataAttributes() %}
                         data-{{ sName }}="{{ sValue }}"
diff --git a/templates/base/components/collapsible-section/layout.html.twig b/templates/base/components/collapsible-section/layout.html.twig
index ea9ae32e4..9dacd7caf 100644
--- a/templates/base/components/collapsible-section/layout.html.twig
+++ b/templates/base/components/collapsible-section/layout.html.twig
@@ -1,5 +1,5 @@
 <div id="{{ oUIBlock.GetId() }}"
-	 class="ibo-collapsible-section {{ oUIBlock.GetCSSClasses() }}{% if oUIBlock.IsOpenedByDefault() %} ibo-is-opened{% endif %}{% if oUIBlock.IsHidden() %} ibo-is-hidden{% endif %}">
+	 class="ibo-collapsible-section {{ oUIBlock.GetAdditionalCSSClass() }}{% if oUIBlock.IsOpenedByDefault() %} ibo-is-opened{% endif %}{% if oUIBlock.IsHidden() %} ibo-is-hidden{% endif %}">
 	<div class="ibo-collapsible-section--header" data-role="ibo-collapsible-section--collapse-toggler">
 		<div class="ibo-collapsible-section--action-button ibo-collapsible-section--maximize-button"><i
 					class="fas fa-caret-down"></i></div>
diff --git a/templates/base/components/panel/layout.html.twig b/templates/base/components/panel/layout.html.twig
index b45c52471..15b52b01c 100644
--- a/templates/base/components/panel/layout.html.twig
+++ b/templates/base/components/panel/layout.html.twig
@@ -1,7 +1,7 @@
 {# @copyright   Copyright (C) 2010-2020 Combodo SARL #}
 {# @license     http://opensource.org/licenses/AGPL-3.0 #}
 {% apply spaceless %}
-    <div id="{{ oUIBlock.GetId() }}" class="ibo-panel ibo-is-{{ oUIBlock.GetColor() }} {{ oUIBlock.GetCSSClasses() }}{% if oUIBlock.IsHidden() %} ibo-is-hidden{% endif %}" {% block iboPanelMetaData %}{% endblock %}>
+    <div id="{{ oUIBlock.GetId() }}" class="ibo-panel ibo-is-{{ oUIBlock.GetColor() }} {{ oUIBlock.GetAdditionalCSSClass() }}{% if oUIBlock.IsHidden() %} ibo-is-hidden{% endif %}" {% block iboPanelMetaData %}{% endblock %}>
         <div class="ibo-panel--header">
             {% block iboPanelHeader %}
                 <div class="ibo-panel--header-left">
diff --git a/templates/base/layouts/content-block/layout.html.twig b/templates/base/layouts/content-block/layout.html.twig
index 92f3d4dc2..e64a0ae7b 100644
--- a/templates/base/layouts/content-block/layout.html.twig
+++ b/templates/base/layouts/content-block/layout.html.twig
@@ -3,12 +3,12 @@
 {# Content Block #}
 {% apply spaceless %}
 
-    {% set bHasDiv = (oUIBlock.GetCSSClasses() or oUIBlock.GetDataAttributes()) %}
+    {% set bHasDiv = (oUIBlock.GetAdditionalCSSClass() or oUIBlock.GetDataAttributes()) %}
 
     {% block iboContentBlockContainer %}
         {% if bHasDiv %}
             <div id="{{ oUIBlock.GetId() }}"
-            class="{% if oUIBlock.GetCSSClasses() %}{{ oUIBlock.GetCSSClasses() }}{% endif %}{% if oUIBlock.IsHidden() %} ibo-is-hidden{% endif %}"
+            class="{% if oUIBlock.GetAdditionalCSSClass() %}{{ oUIBlock.GetCSSClasses() }}{% endif %}{% if oUIBlock.IsHidden() %} ibo-is-hidden{% endif %}"
             {% if oUIBlock.GetDataAttributes() %}
                 {% for sName, sValue in oUIBlock.GetDataAttributes() %}
                     data-{{ sName }}="{{ sValue }}"