diff --git a/css/swad_desktop.css b/css/swad_desktop.css
index 4e27e9c18..0ee73f2ac 100644
--- a/css/swad_desktop.css
+++ b/css/swad_desktop.css
@@ -302,12 +302,23 @@ hr.YELLOW_SEPARA	{height:0; border-top:0; border-bottom:#BD4815 dotted 1px;}
 	display:table;
 	width:100%;
 	}
-.LEFT_RIGHT_COL
+.LEFT_COL
 	{
 	display:table-cell;
 	width:160px;
 	text-align:center;
 	vertical-align:top;
+	position:absolute;
+	left:0;
+	}
+.RIGHT_COL
+	{
+	display:table-cell;
+	width:160px;
+	text-align:center;
+	vertical-align:top;
+	position:absolute;
+	right:0;
 	}
 .LEFT_RIGHT_CELL
 	{
@@ -319,26 +330,57 @@ hr.YELLOW_SEPARA	{height:0; border-top:0; border-bottom:#BD4815 dotted 1px;}
 	{
 	width:138px;
 	}
-#main_zone_central
+
+@media only screen and (max-width: 1280px) {	/* For mobile phones: */
+	#main_zone_central_none, #main_zone_central_left, #main_zone_central_right, #main_zone_central_both
 	{
 	display:table-cell;
 	text-align:center;
 	vertical-align:top;
 	}
+}
+@media only screen and (min-width: 1280px) {	/* For desktop: */
+	#main_zone_central_none /* Hide left and right columns */
+	{
+	display:table-cell;
+	text-align:center;
+	vertical-align:top;
+	}
+	#main_zone_central_left /* Show left column, hide right column */
+	{
+	display:table-cell;
+	text-align:center;
+	vertical-align:top;
+	padding-left:160px;
+	}
+	#main_zone_central_right /* Hide left column, show right column */
+	{
+	display:table-cell;
+	text-align:center;
+	vertical-align:top;
+	padding-right:160px;
+	}
+	#main_zone_central_both /* Show both columns */
+	{
+	display:table-cell;
+	text-align:center;
+	vertical-align:top;
+	padding-left:160px;
+	padding-right:160px;
+	}
+}
+
 #main_zone_central_container
 	{
 	min-width:925px;
 	min-height:925px;
-	width:100%;
 	margin:-8px 0 0 0;
 	padding:10px 0;
 	border-radius:6px;
 	box-shadow:inset -2px -2px 1px 0 rgba(50,50,50,0.2);
 	text-align:center;
 	vertical-align:top;
-	overflow:hidden;
 	position:relative;
-	display:inline-block;
 	}
 #main_zone_central_content
 	{
diff --git a/swad_changelog.h b/swad_changelog.h
index b59853782..b427f6970 100644
--- a/swad_changelog.h
+++ b/swad_changelog.h
@@ -115,11 +115,12 @@
 /****************************** Public constants *****************************/
 /*****************************************************************************/
 
-#define Log_PLATFORM_VERSION	"SWAD 15.45.15 (2015/11/25)"
+#define Log_PLATFORM_VERSION	"SWAD 15.46 (2015/11/27)"
 
 // Number of lines (includes comments but not blank lines) has been got with the following command:
 // nl swad*.c swad*.h css/swad*.css py/swad*.py js/swad*.js soap/swad*.h sql/swad*.sql | tail -1
 /*
+        Version 15.46:    Nov 27, 2015	First version with responsive design: both side columns are hidden when screen size is small. (188078 lines)
         Version 15.45.15: Nov 25, 2015	Some CSS styles related to layout are moved to CSS file. (188021 lines)
         Version 15.45.14: Nov 25, 2015	Some CSS styles related to layout are moved to CSS file. (188037 lines)
         Version 15.45.13: Nov 25, 2015	Some CSS styles related to layout are moved to CSS file. (188059 lines)
diff --git a/swad_global.c b/swad_global.c
index e0443fd01..7a7a5a52b 100644
--- a/swad_global.c
+++ b/swad_global.c
@@ -130,7 +130,6 @@ void Gbl_InitializeGlobals (void)
    Gbl.Prefs.FirstDayOfWeek = Cal_FIRST_DAY_OF_WEEK_DEFAULT;	// Default first day of week
    Gbl.Prefs.Layout = Lay_LAYOUT_DEFAULT;	// Default layout
    Gbl.Prefs.Menu = Mnu_MENU_DEFAULT;		// Default menu
-   Gbl.Prefs.SideCols = Cfg_DEFAULT_COLUMNS;	// Show both side columns, left and right
    Gbl.Prefs.Theme = The_THEME_DEFAULT;		// Default theme
    Gbl.Prefs.IconSet = Ico_ICON_SET_DEFAULT;	// Default icon set
    sprintf (Gbl.Prefs.IconsURL,"%s/%s",
diff --git a/swad_layout.c b/swad_layout.c
index ab5fd078c..18a35caeb 100644
--- a/swad_layout.c
+++ b/swad_layout.c
@@ -177,6 +177,10 @@ void Lay_WriteStartOfPage (void)
             Txt_STR_LANG_ID[Gbl.Prefs.Language],
             Cfg_PLATFORM_SHORT_NAME);
 
+   /* Viewport (used for responsive design) */
+   fprintf (Gbl.F.Out,"<meta name=\"viewport\""
+	              " content=\"width=device-width, initial-scale=1.0\">\n");
+
    /* Title */
    Lay_WritePageTitle ();
 
@@ -257,16 +261,6 @@ void Lay_WriteStartOfPage (void)
       return;
      }
 
-   if (Act_Actions[Gbl.CurrentAct].BrowserWindow == Act_MAIN_WINDOW)
-      fprintf (Gbl.F.Out,"<div id=\"zoomLyr\" class=\"ZOOM\">"
-                         "<img id=\"zoomImg\" src=\"%s/_.gif\""
-                         " alt=\"\" title=\"\""
-                         " class=\"IMG_USR\" />"
-                         "<div id=\"zoomTxt\" class=\"CENTER_MIDDLE\">"
-                         "</div>"
-                         "</div>",
-	       Gbl.Prefs.IconsURL);
-
    /***** Start of box that contains the whole page except the foot *****/
    fprintf (Gbl.F.Out,"<div id=\"%s\">",IdWholePage[Gbl.Prefs.Theme]);
 
@@ -290,23 +284,48 @@ void Lay_WriteStartOfPage (void)
    if (Gbl.Prefs.Layout == Lay_LAYOUT_DESKTOP)
       if (Gbl.Prefs.SideCols & Lay_SHOW_LEFT_COLUMN)		// Left column visible
 	{
-	 fprintf (Gbl.F.Out,"<div class=\"LEFT_RIGHT_COL\">");
+	 fprintf (Gbl.F.Out,"<div class=\"LEFT_COL\">");
 	 Lay_ShowLeftColumn ();
 	 fprintf (Gbl.F.Out,"</div>");
 	}
 
+   /* Right column */
+   if (Gbl.Prefs.Layout == Lay_LAYOUT_DESKTOP)
+      if (Gbl.Prefs.SideCols & Lay_SHOW_RIGHT_COLUMN)	// Right column visible
+	{
+	 fprintf (Gbl.F.Out,"<div class=\"RIGHT_COL\">");
+	 Lay_ShowRightColumn ();
+	 fprintf (Gbl.F.Out,"</div>");
+	}
+
    /* Central (main) part */
-   fprintf (Gbl.F.Out,"<div id=\"main_zone_central\">"
-		      "<div id=\"main_zone_central_container\" class=\"%s\">"
+   switch (Gbl.Prefs.SideCols)
+     {
+      case 0:
+         fprintf (Gbl.F.Out,"<div id=\"main_zone_central_none\">");
+	 break;
+      case Lay_SHOW_LEFT_COLUMN:
+         fprintf (Gbl.F.Out,"<div id=\"main_zone_central_left\">");
+	 break;
+      case Lay_SHOW_RIGHT_COLUMN:
+         fprintf (Gbl.F.Out,"<div id=\"main_zone_central_right\">");
+	 break;
+      case (Lay_SHOW_LEFT_COLUMN | Lay_SHOW_RIGHT_COLUMN):
+         fprintf (Gbl.F.Out,"<div id=\"main_zone_central_both\">");
+         break;
+     }
+   fprintf (Gbl.F.Out,"<div id=\"main_zone_central_container\" class=\"%s\">"
 		      "<div id=\"main_zone_central_content\">",
 	    The_TabOnBgColors[Gbl.Prefs.Theme]);
    switch (Gbl.Prefs.Layout)
      {
       case Lay_LAYOUT_DESKTOP:
          /* Left bar used to expand-contract central zone */
+	 /*
          fprintf (Gbl.F.Out,"<div class=\"MAIN_ZONE_EXPAND\">");
          Pre_PutLeftIconToHideShowCols ();
          fprintf (Gbl.F.Out,"</div>");
+         */
 
          if (Gbl.Prefs.Menu == Mnu_MENU_VERTICAL)
            {
@@ -381,31 +400,25 @@ static void Lay_WriteEndOfPage (void)
    if (!Gbl.Layout.TablEndWritten)
      {
       Gbl.Layout.TablEndWritten = true;
-      fprintf (Gbl.F.Out,"</div>");
+      fprintf (Gbl.F.Out,"</div>");	// main_zone_canvas
 
+      /*
       if (Gbl.Prefs.Layout == Lay_LAYOUT_DESKTOP)
 	{
-	 /* Right bar used to expand-contract central zone */
+	 // Right bar used to expand-contract central zone
 	 fprintf (Gbl.F.Out,"<div id=\"MAIN_ZONE_EXPAND\">");
 	 Pre_PutRigthIconToHideShowCols ();
 	 fprintf (Gbl.F.Out,"</div>");
 	}
+      */
 
-      fprintf (Gbl.F.Out,"</div>"
-			 "</div>"
-			 "</div>");
-
-      /* Right column */
-      if (Gbl.Prefs.Layout == Lay_LAYOUT_DESKTOP)
-	 if (Gbl.Prefs.SideCols & Lay_SHOW_RIGHT_COLUMN)	// Right column visible
-	   {
-	    fprintf (Gbl.F.Out,"<div class=\"LEFT_RIGHT_COL\">");
-	    Lay_ShowRightColumn ();
-	    fprintf (Gbl.F.Out,"</div>");
-	   }
+      fprintf (Gbl.F.Out,"</div>"	// main_zone_central_content
+			 "</div>"	// main_zone_central_container
+			 "</div>"	// main_zone_central
+			 "</div>");	// main_zone
 
       /***** End of box that contains the whole page except the foot *****/
-      fprintf (Gbl.F.Out,"</div>\n");
+      fprintf (Gbl.F.Out,"</div>\n");	// whole_page_*
      }
   }
 
@@ -769,7 +782,7 @@ static void Lay_WritePageTopHeadingDesktop (void)
       Usr_PutFormLogIn ();
    fprintf (Gbl.F.Out,"</div>");
 
-   /* Start of 1st. row */
+   /* End of 1st. row */
    fprintf (Gbl.F.Out,"</div>");
 
    /***** 2nd. row *****/