diff --git a/css/swad21.70.1.css b/css/swad21.70.1.css
index 7866d72e8..17de3bd8d 100644
--- a/css/swad21.70.1.css
+++ b/css/swad21.70.1.css
@@ -1850,10 +1850,17 @@ a:hover img.CENTER_PHOTO_SHOW
 	box-sizing:border-box;
 	margin:8px auto;
 	padding:12px;
-	background-color:#fff8e5;
 	border-radius:2px;
 	box-shadow: 0 2px 2px 0 rgba(0,0,0,0.14), 0 2px 1px -2px rgba(0,0,0,0.2), 0 1px 5px 0 rgba(0,0,0,0.12);
 	}
+.ALERT_BG_WHITE		{background-color:#fff8e5;}
+.ALERT_BG_GREY		{background-color:#fff8e5;}
+.ALERT_BG_PURPLE	{background-color:#fff8e5;}
+.ALERT_BG_BLUE		{background-color:#fff8e5;}
+.ALERT_BG_YELLOW	{background-color:#fff8e5;}
+.ALERT_BG_PINK		{background-color:#fff8e5;}
+.ALERT_BG_DARK		{background-color:#a0a0a0;}
+
 .ALERT_CLOSE
 	{
 	float:right;
diff --git a/swad_alert.c b/swad_alert.c
index 341b82d0d..7466f55c2 100644
--- a/swad_alert.c
+++ b/swad_alert.c
@@ -359,6 +359,7 @@ void Ale_ShowAlertAndButton1 (Ale_AlertType_t AlertType,const char *fmt,...)
 
 static void Ale_ShowFixAlertAndButton1 (Ale_AlertType_t AlertType,const char *Txt)
   {
+   extern const char *The_ClassAlertBackground[The_NUM_THEMES];
    extern const char *Txt_Close;
    char IdAlert[Frm_MAX_BYTES_ID + 1];
    static const bool AlertClosable[Ale_NUM_ALERT_TYPES] =
@@ -386,7 +387,7 @@ static void Ale_ShowFixAlertAndButton1 (Ale_AlertType_t AlertType,const char *Tx
    if (!Gbl.Layout.HTMLStartWritten)
       Lay_WriteStartOfPage ();
 
-   /***** Begin box *****/
+   /***** Begin container *****/
    if (AlertClosable[AlertType])
      {
       /* Create unique id for alert */
@@ -395,27 +396,30 @@ static void Ale_ShowFixAlertAndButton1 (Ale_AlertType_t AlertType,const char *Tx
      }
    else
       HTM_DIV_Begin ("class=\"CM\"");
-   HTM_DIV_Begin ("class=\"ALERT\"");
 
-   /***** Icon to close the alert *****/
-   if (AlertClosable[AlertType])
-     {
-      HTM_DIV_Begin ("class=\"ALERT_CLOSE\"");
-	 HTM_A_Begin ("href=\"\" onclick=\"toggleDisplay('%s');return false;\" /",
-		      IdAlert);
-	    Ico_PutIcon ("times.svg",Txt_Close,"ICO16x16");
-	 HTM_A_End ();
+   /***** Begin box *****/
+   HTM_DIV_Begin ("class=\"ALERT %s\"",
+                  The_ClassAlertBackground[Gbl.Prefs.Theme]);
+
+      /***** Icon to close the alert *****/
+      if (AlertClosable[AlertType])
+	{
+	 HTM_DIV_Begin ("class=\"ALERT_CLOSE\"");
+	    HTM_A_Begin ("href=\"\" onclick=\"toggleDisplay('%s');return false;\" /",
+			 IdAlert);
+	       Ico_PutIcon ("times.svg",Txt_Close,"ICO16x16");
+	    HTM_A_End ();
+	 HTM_DIV_End ();
+	}
+
+      /***** Write message *****/
+      if (AlertType == Ale_NONE)
+	 HTM_DIV_Begin ("class=\"ALERT_TXT\"");
+      else
+	 HTM_DIV_Begin ("class=\"ALERT_TXT\" style=\"background-image:url('%s/%s');\"",
+			Cfg_URL_ICON_PUBLIC,Ale_AlertIcons[AlertType]);
+      HTM_Txt (Txt);
       HTM_DIV_End ();
-     }
-
-   /***** Write message *****/
-   if (AlertType == Ale_NONE)
-      HTM_DIV_Begin ("class=\"ALERT_TXT\"");
-   else
-      HTM_DIV_Begin ("class=\"ALERT_TXT\" style=\"background-image:url('%s/%s');\"",
-	             Cfg_URL_ICON_PUBLIC,Ale_AlertIcons[AlertType]);
-   HTM_Txt (Txt);
-   HTM_DIV_End ();
   }
 
 /*****************************************************************************/
@@ -426,28 +430,30 @@ void Ale_ShowAlertAndButton2 (Act_Action_t NextAction,const char *Anchor,const c
                               void (*FuncParams) (void *Args),void *Args,
                               Btn_Button_t Button,const char *TxtButton)
   {
-   /***** Optional button *****/
-   if (NextAction != ActUnk &&
-       Button != Btn_NO_BUTTON &&
-       TxtButton)
-      if (TxtButton[0])
-	{
-         /* Begin form */
-         Frm_BeginFormAnchorOnSubmit (NextAction,Anchor,OnSubmit);
-	    if (FuncParams)
-	      {
-	       FuncParams (Args);
-	      }
+      /***** Optional button *****/
+      if (NextAction != ActUnk &&
+	  Button != Btn_NO_BUTTON &&
+	  TxtButton)
+	 if (TxtButton[0])
+	   {
+	    /* Begin form */
+	    Frm_BeginFormAnchorOnSubmit (NextAction,Anchor,OnSubmit);
+	       if (FuncParams)
+		 {
+		  FuncParams (Args);
+		 }
 
-	    /* Put button */
-	    Btn_PutButton (Button,TxtButton);
+	       /* Put button */
+	       Btn_PutButton (Button,TxtButton);
 
-         /* End form */
-	 Frm_EndForm ();
-	}
+	    /* End form */
+	    Frm_EndForm ();
+	   }
 
-   /***** End box *****/
-   HTM_DIV_End ();
+      /***** End box *****/
+      HTM_DIV_End ();
+
+   /***** End container *****/
    HTM_DIV_End ();
   }
 
diff --git a/swad_changelog.h b/swad_changelog.h
index 46cfafbbc..68f30b3d4 100644
--- a/swad_changelog.h
+++ b/swad_changelog.h
@@ -602,7 +602,7 @@ TODO: FIX BUG, URGENT! En las fechas como par
 
 TODO: En las encuestas, que los estudiantes no puedan ver los resultados hasta que no finalice el plazo.
 */
-#define Log_PLATFORM_VERSION	"SWAD 21.70.4 (2021-12-18)"
+#define Log_PLATFORM_VERSION	"SWAD 21.70.6 (2021-12-20)"
 #define CSS_FILE		"swad21.70.1.css"
 #define JS_FILE			"swad21.67.4.js"
 /*
diff --git a/swad_theme.c b/swad_theme.c
index b5298763d..6e0b0ba37 100644
--- a/swad_theme.c
+++ b/swad_theme.c
@@ -393,6 +393,17 @@ const char *The_ClassFrameTitleColor[The_NUM_THEMES] =
    [The_THEME_DARK  ] = "FRAME_TITLE_DARK",
   };
 
+const char *The_ClassAlertBackground[The_NUM_THEMES] =
+  {
+   [The_THEME_WHITE ] = "ALERT_BG_WHITE",
+   [The_THEME_GREY  ] = "ALERT_BG_GREY",
+   [The_THEME_PURPLE] = "ALERT_BG_PURPLE",
+   [The_THEME_BLUE  ] = "ALERT_BG_BLUE",
+   [The_THEME_YELLOW] = "ALERT_BG_YELLOW",
+   [The_THEME_PINK  ] = "ALERT_BG_PINK",
+   [The_THEME_DARK  ] = "ALERT_BG_DARK",
+  };
+
 /*****************************************************************************/
 /****************************** Private prototypes ***************************/
 /*****************************************************************************/