diff --git a/app/controllers/problems_controller.rb b/app/controllers/problems_controller.rb
--- a/app/controllers/problems_controller.rb
+++ b/app/controllers/problems_controller.rb
@@ -75,7 +75,7 @@
       end
       @problem.description = @description
     elsif @description
-      if !@description.update_attributes(description_params)
+      if !@description.update(description_params)
         flash[:notice] = 'Error saving description'
         render :action => 'edit' and return
       end
@@ -84,7 +84,7 @@
         flash[:notice] = 'Error: Uploaded file is not PDF'
         render :action => 'edit' and return
     end
-    if @problem.update_attributes(problem_params)
+    if @problem.update(problem_params)
       flash[:notice] = 'Problem was successfully updated.'
       unless params[:file] == nil or params[:file] == ''
         flash[:notice] = 'Problem was successfully updated and a new PDF file is uploaded.'
@@ -117,7 +117,7 @@
 
   def toggle
     @problem = Problem.find(params[:id])
-    @problem.update_attributes(available: !(@problem.available) )
+    @problem.update(available: !(@problem.available) )
     respond_to do |format|
       format.js { }
     end
@@ -125,7 +125,7 @@
 
   def toggle_test
     @problem = Problem.find(params[:id])
-    @problem.update_attributes(test_allowed: !(@problem.test_allowed?) )
+    @problem.update(test_allowed: !(@problem.test_allowed?) )
     respond_to do |format|
       format.js { }
     end
@@ -133,7 +133,7 @@
 
   def toggle_view_testcase
     @problem = Problem.find(params[:id])
-    @problem.update_attributes(view_testcase: !(@problem.view_testcase?) )
+    @problem.update(view_testcase: !(@problem.view_testcase?) )
     respond_to do |format|
       format.js { }
     end
diff --git a/app/views/layouts/_header.html.haml b/app/views/layouts/_header.html.haml
--- a/app/views/layouts/_header.html.haml
+++ b/app/views/layouts/_header.html.haml
@@ -10,7 +10,7 @@
         %ul.navbar-nav.me-auto.mb-2.mb-lg-0
           / submission
           - if (@current_user!=nil) and (GraderConfiguration.show_tasks_to?(@current_user))
-            %li.nav-item.dropdown
+            %li.nav-item.dropdown.mx-2
               %a.nav-link.dropdown-toggle{href: '#', 'data-bs': {toggle:'dropdown'},  aria: {expanded:"false"}, role: "button"}
                 = "#{I18n.t 'menu.submissions'}"
               %ul.dropdown-menu
@@ -18,23 +18,23 @@
                 %li= link_to 'Self Test', test_index_path, class:'dropdown-item'
           / hall of fame
           - if GraderConfiguration['right.user_hall_of_fame']
-            = add_menu("#{I18n.t 'menu.hall_of_fame'}", 'report', 'problem_hof', class: 'nav-item')
+            %li= link_to "#{I18n.t 'menu.hall_of_fame'}", problem_hof_report_path, class: 'nav-link mx-2'
           / display MODE button (with countdown in contest mode)
           - if GraderConfiguration.analysis_mode?
-            %div.navbar-btn.btn.btn-success#countdown= "ANALYSIS MODE"
+            %div.btn.btn-success#countdown= "ANALYSIS MODE"
           - elsif GraderConfiguration.time_limit_mode?
             - if @current_user.contest_finished?
-              %div.navbar-btn.btn.btn-danger#countdown= "Contest is over"
+              %div.btn.btn-danger#countdown= "Contest is over"
             - elsif !@current_user.contest_started?
-              %div.navbar-btn.btn.btn-primary#countdown= (t 'title_bar.contest_not_started')
+              %div.btn.btn-primary#countdown= (t 'title_bar.contest_not_started')
             - else
-              %div.navbar-btn.btn.btn-primary#countdown asdf
+              %div.btn.btn-primary#countdown asdf
               :javascript
                 $("#countdown").countdown({until: "+#{@current_user.contest_time_left.to_i}s", layout: 'Time left: {hnn}:{mnn}:{snn}'}); 
           / admin section
           - if (@current_user!=nil) and (session[:admin])
             / management
-            %li.nav-item.dropdown
+            %li.nav-item.dropdown.mx-2
               %a.nav-link.dropdown-toggle{href: '#', 'data-bs': {toggle:'dropdown'},  aria: {haspopup:"true", expanded:"false"}, role: "button"}
                 Manage
               %ul.dropdown-menu
@@ -54,7 +54,7 @@
                 %li= link_to 'Contests', contest_management_index_path, class: 'dropdown-item'
                 -#
             / report
-            %li.nav-item.dropdown
+            %li.nav-item.dropdown.mx-2
               %a.nav-link.dropdown-toggle{href: '#', 'data-bs': {toggle:'dropdown'},  aria: {haspopup:"true", expanded:"false"}, role: "button"}
                 Report
               %ul.dropdown-menu
diff --git a/app/views/main/_submission_box.html.haml b/app/views/main/_submission_box.html.haml
--- a/app/views/main/_submission_box.html.haml
+++ b/app/views/main/_submission_box.html.haml
@@ -1,4 +1,4 @@
-= form_tag({:action => 'submit'}, :multipart => true, class: 'form') do
+= form_with url: submit_main_path, multipart: true, class: 'form' do |form|
   - if @submission and @submission.errors.any?
     #error_explanation
       .alert.alert-danger
@@ -6,15 +6,14 @@
         %ul
           - @submission.errors.full_messages.each do |msg|
             %li= msg
-  .form-group
-    = label_tag :submission, 'Problem:'
-    = select 'submission', 'problem_id', [[(t 'main.specified_in_header'),'-1']] + @problems.collect {|p| ["[#{p.name}] #{p.full_name}", p.id]}, {:selected => '-1'}, { class: 'select2 form-control', style: "width: 100%" }
-  .form-group
-    = label_tag :file, 'File:'
-    .input-group
-      %span.input-group-btn
-        %span.btn.btn-default.btn-file
-          Browse
-          = file_field_tag 'file'
-      = text_field_tag '' , nil, {readonly: true, class: 'form-control'}
-  = submit_tag 'Submit', class: 'btn btn-default'
+  .row.mb-2
+    .col-sm-2
+      = form.label :submission, 'Problem:', class: 'form-label'
+    .col-sm-10
+      = select 'submission', 'problem_id', [[(t 'main.specified_in_header'),'-1']] + @problems.collect {|p| ["[#{p.name}] #{p.full_name}", p.id]}, {:selected => '-1'}, { class: 'select2 form-control', style: "width: 100%" }
+  .row.mb-2
+    .col-sm-2
+      = form.label :file, 'File:', class: 'form-label'
+    .col-sm-10
+      = form.file_field :file, class: 'form-control'
+  = form.submit 'Submit', class: 'btn btn-primary'
diff --git a/app/views/main/list.html.haml b/app/views/main/list.html.haml
--- a/app/views/main/list.html.haml
+++ b/app/views/main/list.html.haml
@@ -13,11 +13,11 @@
 .row
   .col-md-7
     - if GraderConfiguration.show_submitbox_to?(@user)
-      .panel.panel-primary
-        .panel-heading
+      .card.border-primary
+        .card-header.text-bg-primary
           Submission
-        .panel-body
-          = render :partial => 'submission_box'
+        .card-body
+          = render 'submission_box'
     - if GraderConfiguration.show_tasks_to?(@user)
       - if not GraderConfiguration.multicontests?
         %table.table.table-striped.table-condensed
diff --git a/app/views/report/_score_table.html.haml b/app/views/report/_score_table.html.haml
--- a/app/views/report/_score_table.html.haml
+++ b/app/views/report/_score_table.html.haml
@@ -1,4 +1,4 @@
-%table.table.sortable.table-striped.table-bordered.table-condensed
+%table#score-table.table.sortable.table-striped.table-bordered.table-condensed
   %thead
     %tr
       %th Login