diff --git a/application/views/appointments/cookie_notice_modal.php b/application/views/appointments/cookie_notice_modal.php
index 437296cd..3293c760 100644
--- a/application/views/appointments/cookie_notice_modal.php
+++ b/application/views/appointments/cookie_notice_modal.php
@@ -9,7 +9,7 @@
                 <p><?= $cookie_notice_content ?></p>
             </div>
             <div class="modal-footer">
-                <button type="button" class="btn btn-default" data-dismiss="modal"><?= lang('close') ?></button>
+                <button type="button" class="btn btn-light" data-dismiss="modal"><?= lang('close') ?></button>
             </div>
         </div>
     </div>
diff --git a/application/views/appointments/privacy_policy_modal.php b/application/views/appointments/privacy_policy_modal.php
index dae2983d..0ea6e0c8 100644
--- a/application/views/appointments/privacy_policy_modal.php
+++ b/application/views/appointments/privacy_policy_modal.php
@@ -9,7 +9,7 @@
                 <p><?= $privacy_policy_content ?></p>
             </div>
             <div class="modal-footer">
-                <button type="button" class="btn btn-default" data-dismiss="modal"><?= lang('close') ?></button>
+                <button type="button" class="btn btn-light" data-dismiss="modal"><?= lang('close') ?></button>
             </div>
         </div>
     </div>
diff --git a/application/views/appointments/terms_and_conditions_modal.php b/application/views/appointments/terms_and_conditions_modal.php
index ad4a22f5..e167f4fd 100644
--- a/application/views/appointments/terms_and_conditions_modal.php
+++ b/application/views/appointments/terms_and_conditions_modal.php
@@ -9,7 +9,7 @@
                 <p><?= $terms_and_conditions_content ?></p>
             </div>
             <div class="modal-footer">
-                <button type="button" class="btn btn-default" data-dismiss="modal"><?= lang('close') ?></button>
+                <button type="button" class="btn btn-light" data-dismiss="modal"><?= lang('close') ?></button>
             </div>
         </div>
     </div>
diff --git a/application/views/backend/calendar.php b/application/views/backend/calendar.php
index 51112357..121863a5 100755
--- a/application/views/backend/calendar.php
+++ b/application/views/backend/calendar.php
@@ -440,7 +440,7 @@
             </div>
             <div class="modal-footer">
                 <button id="save-extra" class="btn btn-primary"><?= lang('save') ?></button>
-                <button id="cancel-extra" class="btn btn-default" data-dismiss="modal"><?= lang('cancel') ?></button>
+                <button id="cancel-extra" class="btn btn-light" data-dismiss="modal"><?= lang('cancel') ?></button>
             </div>
         </div>
     </div>
diff --git a/application/views/backend/settings.php b/application/views/backend/settings.php
index e9fbdb3a..faa0d326 100755
--- a/application/views/backend/settings.php
+++ b/application/views/backend/settings.php
@@ -194,7 +194,7 @@
                                     <?= lang('phone_number') ?>
                                 </label>
                                 <br>
-                                <button type="button" id="require-phone-number" class="btn btn-default" data-toggle="button" aria-pressed="false">
+                                <button type="button" id="require-phone-number" class="btn btn-light" data-toggle="button" aria-pressed="false">
                                     <span class="glyphicon glyphicon-phone-alt"></span>
                                     <?= lang('require_phone_number') ?>
                                 </button>
@@ -205,7 +205,7 @@
                             <div class="form-group">
                                 <label><?= lang('any_provider') ?></label>
                                 <br>
-                                <button type="button" id="display-any-provider" class="btn btn-default" data-toggle="button" aria-pressed="false">
+                                <button type="button" id="display-any-provider" class="btn btn-light" data-toggle="button" aria-pressed="false">
                                     <span class="glyphicon glyphicon-user"></span>
                                     <?= lang('display_any_provider') ?>
                                 </button>
@@ -255,7 +255,7 @@
                             </table>
 
                             <div class="text-right">
-                                <button class="btn btn-default" id="apply-global-working-plan" type="button">
+                                <button class="btn btn-light" id="apply-global-working-plan" type="button">
                                     <span class="glyphicon glyphicon-ok"></span>
                                     <?= lang('apply_to_all_providers') ?>
                                 </button>
diff --git a/application/views/general/error404.php b/application/views/general/error404.php
index 9e414f4a..fc54486f 100644
--- a/application/views/general/error404.php
+++ b/application/views/general/error404.php
@@ -75,7 +75,7 @@
             <?= lang('book_appointment_title') ?>
         </a>
 
-        <a href="<?= site_url('backend') ?>" class="btn btn-default btn-large">
+        <a href="<?= site_url('backend') ?>" class="btn btn-light btn-large">
             <i class="fas fa-wrench"></i>
             <?= lang('backend_section') ?>
         </a>
diff --git a/application/views/general/update.php b/application/views/general/update.php
index af1e0152..87ace1df 100644
--- a/application/views/general/update.php
+++ b/application/views/general/update.php
@@ -71,7 +71,7 @@
         <?php endif; ?>
 
         <div>
-            <a href="<?= site_url('backend') ?>" class="btn btn-default btn-large">
+            <a href="<?= site_url('backend') ?>" class="btn btn-light btn-large">
                 <i class="fas fa-wrench"></i>
                 <?= lang('backend_section') ?>
             </a>
diff --git a/assets/js/backend.js b/assets/js/backend.js
index 19ae4bd9..0653122e 100644
--- a/assets/js/backend.js
+++ b/assets/js/backend.js
@@ -139,7 +139,7 @@ window.Backend = window.Backend || {};
 
         actions.forEach(function(action) {
             $('<button/>', {
-                'class': 'btn btn-default btn-xs',
+                'class': 'btn btn-light btn-xs',
                 'text': action.label,
                 'on': {
                     'click': action.function
diff --git a/assets/js/backend_calendar.js b/assets/js/backend_calendar.js
index 5c9b260c..45253c3a 100755
--- a/assets/js/backend_calendar.js
+++ b/assets/js/backend_calendar.js
@@ -47,7 +47,7 @@ window.BackendCalendar = window.BackendCalendar || {};
 
                 $toggleFullscreen
                     .removeClass('btn-success')
-                    .addClass('btn-default');
+                    .addClass('btn-light');
             } else {
                 // Switch to fullscreen mode.
                 if (element.requestFullscreen) {
@@ -60,7 +60,7 @@ window.BackendCalendar = window.BackendCalendar || {};
                     element.webkitRequestFullscreen();
                 }
                 $toggleFullscreen
-                    .removeClass('btn-default')
+                    .removeClass('btn-light')
                     .addClass('btn-success');
             }
         });
diff --git a/assets/js/backend_calendar_default_view.js b/assets/js/backend_calendar_default_view.js
index ce1994b7..0388281e 100755
--- a/assets/js/backend_calendar_default_view.js
+++ b/assets/js/backend_calendar_default_view.js
@@ -338,7 +338,7 @@ window.BackendCalendarDefaultView = window.BackendCalendarDefaultView || {};
                                 'text': EALang.delete
                             }),
                             $('<button/>', {
-                                'class': 'close-popover btn btn-default',
+                                'class': 'close-popover btn btn-light',
                                 'text': EALang.close
                             })
                         ]
@@ -402,7 +402,7 @@ window.BackendCalendarDefaultView = window.BackendCalendarDefaultView || {};
                                 'text': EALang.delete
                             }),
                             $('<button/>', {
-                                'class': 'close-popover btn btn-default',
+                                'class': 'close-popover btn btn-light',
                                 'text': EALang.close
                             })
                         ]
@@ -499,7 +499,7 @@ window.BackendCalendarDefaultView = window.BackendCalendarDefaultView || {};
                                 'text': EALang.delete
                             }),
                             $('<button/>', {
-                                'class': 'close-popover btn btn-default',
+                                'class': 'close-popover btn btn-light',
                                 'text': EALang.close
                             })
                         ]
diff --git a/assets/js/backend_calendar_table_view.js b/assets/js/backend_calendar_table_view.js
index 7d5e3725..b3dc0d77 100755
--- a/assets/js/backend_calendar_table_view.js
+++ b/assets/js/backend_calendar_table_view.js
@@ -314,7 +314,7 @@ window.BackendCalendarTableView = window.BackendCalendarTableView || {};
             .appendTo('#calendar');
 
         $('<button/>', {
-            'class': 'btn btn-xs btn-default previous',
+            'class': 'btn btn-xs btn-light previous',
             'html': [
                 $('<span/>', {
                     'class': 'glyphicon glyphicon-chevron-left'
@@ -331,7 +331,7 @@ window.BackendCalendarTableView = window.BackendCalendarTableView || {};
             .appendTo($calendarHeader);
 
         $('<button/>', {
-            'class': 'btn btn-xs btn-default next',
+            'class': 'btn btn-xs btn-light next',
             'html': [
                 $('<span/>', {
                     'class': 'glyphicon glyphicon-chevron-right'
@@ -1065,7 +1065,7 @@ window.BackendCalendarTableView = window.BackendCalendarTableView || {};
                                 'text': EALang.delete
                             }),
                             $('<button/>', {
-                                'class': 'close-popover btn btn-default',
+                                'class': 'close-popover btn btn-light',
                                 'text': EALang.close
                             })
                         ]
@@ -1129,7 +1129,7 @@ window.BackendCalendarTableView = window.BackendCalendarTableView || {};
                                 'text': EALang.delete
                             }),
                             $('<button/>', {
-                                'class': 'close-popover btn btn-default',
+                                'class': 'close-popover btn btn-light',
                                 'text': EALang.close
                             })
                         ]
@@ -1226,7 +1226,7 @@ window.BackendCalendarTableView = window.BackendCalendarTableView || {};
                                 'text': EALang.delete
                             }),
                             $('<button/>', {
-                                'class': 'close-popover btn btn-default',
+                                'class': 'close-popover btn btn-light',
                                 'text': EALang.close
                             })
                         ]
diff --git a/assets/js/general_functions.js b/assets/js/general_functions.js
index ac4d632b..b458ef7e 100755
--- a/assets/js/general_functions.js
+++ b/assets/js/general_functions.js
@@ -80,7 +80,7 @@ window.GeneralFunctions = window.GeneralFunctions || {};
         });
 
         $('#message_box').dialog('open');
-        $('.ui-dialog .ui-dialog-buttonset button').addClass('btn btn-default');
+        $('.ui-dialog .ui-dialog-buttonset button').addClass('btn btn-light');
         $('#message_box .ui-dialog-titlebar-close').hide();
     };
 
diff --git a/assets/js/working_plan.js b/assets/js/working_plan.js
index 66fcf5ed..7b147dc0 100755
--- a/assets/js/working_plan.js
+++ b/assets/js/working_plan.js
@@ -221,7 +221,7 @@
                             'html': [
                                 $('<button/>', {
                                     'type': 'button',
-                                    'class': 'btn btn-default btn-sm edit-extra',
+                                    'class': 'btn btn-light btn-sm edit-extra',
                                     'title': EALang.edit,
                                     'html': [
                                         $('<span/>', {
@@ -231,7 +231,7 @@
                                 }),
                                 $('<button/>', {
                                     'type': 'button',
-                                    'class': 'btn btn-default btn-sm delete-extra',
+                                    'class': 'btn btn-light btn-sm delete-extra',
                                     'title': EALang.delete,
                                     'html': [
                                         $('<span/>', {
@@ -241,7 +241,7 @@
                                 }),
                                 $('<button/>', {
                                     'type': 'button',
-                                    'class': 'btn btn-default btn-sm save-extra d-none',
+                                    'class': 'btn btn-light btn-sm save-extra d-none',
                                     'title': EALang.save,
                                     'html': [
                                         $('<span/>', {
@@ -251,7 +251,7 @@
                                 }),
                                 $('<button/>', {
                                     'type': 'button',
-                                    'class': 'btn btn-default btn-sm cancel-extra d-none',
+                                    'class': 'btn btn-light btn-sm cancel-extra d-none',
                                     'title': EALang.cancel,
                                     'html': [
                                         $('<span/>', {
@@ -580,7 +580,7 @@
                         'html': [
                             $('<button/>', {
                                 'type': 'button',
-                                'class': 'btn btn-default btn-sm edit-extra',
+                                'class': 'btn btn-light btn-sm edit-extra',
                                 'title': EALang.edit,
                                 'html': [
                                     $('<span/>', {
@@ -590,7 +590,7 @@
                             }),
                             $('<button/>', {
                                 'type': 'button',
-                                'class': 'btn btn-default btn-sm delete-extra',
+                                'class': 'btn btn-light btn-sm delete-extra',
                                 'title': EALang.delete,
                                 'html': [
                                     $('<span/>', {
@@ -600,7 +600,7 @@
                             }),
                             $('<button/>', {
                                 'type': 'button',
-                                'class': 'btn btn-default btn-sm save-extra d-none',
+                                'class': 'btn btn-light btn-sm save-extra d-none',
                                 'title': EALang.save,
                                 'html': [
                                     $('<span/>', {
@@ -610,7 +610,7 @@
                             }),
                             $('<button/>', {
                                 'type': 'button',
-                                'class': 'btn btn-default btn-sm cancel-extra d-none',
+                                'class': 'btn btn-light btn-sm cancel-extra d-none',
                                 'title': EALang.cancel,
                                 'html': [
                                     $('<span/>', {