diff --git a/admin/tool/monitor/classes/output/managerules/renderer.php b/admin/tool/monitor/classes/output/managerules/renderer.php
index 5eaed9fde4f..217eab2207e 100644
--- a/admin/tool/monitor/classes/output/managerules/renderer.php
+++ b/admin/tool/monitor/classes/output/managerules/renderer.php
@@ -77,7 +77,7 @@ class renderer extends \plugin_renderer_base {
     protected function render_add_button($courseid) {
         global $CFG;
 
-        $button = \html_writer::tag('button', get_string('addrule', 'tool_monitor'));
+        $button = \html_writer::tag('button', get_string('addrule', 'tool_monitor'), ['class' => 'btn btn-primary']);
         $addurl = new \moodle_url($CFG->wwwroot. '/admin/tool/monitor/edit.php', array('courseid' => $courseid));
         return \html_writer::link($addurl, $button);
     }
diff --git a/admin/tool/spamcleaner/index.php b/admin/tool/spamcleaner/index.php
index ec4b1177c85..27da1b66e36 100644
--- a/admin/tool/spamcleaner/index.php
+++ b/admin/tool/spamcleaner/index.php
@@ -96,12 +96,12 @@ echo $OUTPUT->box_start();     // The forms section at the top
 
 <div class="mdl-align">
 
-<form method="post" action="index.php">
+<form method="post" action="index.php" class="form-inline spamcleanerform">
   <div>
     <label class="accesshide" for="keyword_el"><?php print_string('spamkeyword', 'tool_spamcleaner') ?></label>
-    <input type="text" name="keyword" id="keyword_el" value="<?php p($keyword) ?>" />
+    <input type="text" class="form-control" name="keyword" id="keyword_el" value="<?php p($keyword) ?>" />
     <input type="hidden" name="sesskey" value="<?php echo sesskey();?>" />
-    <input type="submit" value="<?php echo get_string('spamsearch', 'tool_spamcleaner')?>" />
+    <input type="submit" class="btn btn-primary" value="<?php echo get_string('spamsearch', 'tool_spamcleaner')?>" />
   </div>
 </form>
 <p><?php echo get_string('spameg', 'tool_spamcleaner');?></p>
@@ -110,7 +110,8 @@ echo $OUTPUT->box_start();     // The forms section at the top
 
 <form method="post"  action="index.php">
   <div>
-    <input type="submit" name="autodetect" value="<?php echo get_string('spamauto', 'tool_spamcleaner');?>" />
+    <input type="submit" class="btn btn-primary" name="autodetect"
+           value="<?php echo get_string('spamauto', 'tool_spamcleaner');?>" />
   </div>
 </form>
 
@@ -256,7 +257,9 @@ function print_user_list($users_rs, $keywords) {
     foreach ($users_rs as $rs){
         foreach ($rs as $user) {
             if (!$count) {
-                echo '<table border="1" width="100%" id="data-grid"><tr><th>&nbsp;</th><th>'.get_string('user','admin').'</th><th>'.get_string('spamdesc', 'tool_spamcleaner').'</th><th>'.get_string('spamoperation', 'tool_spamcleaner').'</th></tr>';
+                echo '<table class="table table-bordered" border="1" width="100%" id="data-grid"><tr><th>&nbsp;</th>
+                    <th>'.get_string('user', 'admin').'</th><th>'.get_string('spamdesc', 'tool_spamcleaner').'</th>
+                    <th>'.get_string('spamoperation', 'tool_spamcleaner').'</th></tr>';
             }
             $count++;
             filter_user($user, $keywords, $count);
@@ -269,7 +272,7 @@ function print_user_list($users_rs, $keywords) {
     } else {
         echo '</table>';
         echo '<div class="mld-align">
-              <button id="removeall_btn">'.get_string('spamdeleteall', 'tool_spamcleaner').'</button>
+              <button id="removeall_btn" class="btn btn-secondary">'.get_string('spamdeleteall', 'tool_spamcleaner').'</button>
               </div>';
     }
 }
@@ -357,8 +360,10 @@ function print_user_entry($user, $keywords, $count) {
 
         $html .= '<td align="left">'.format_text($user->description, $user->descriptionformat, array('overflowdiv'=>true)).'</td>';
         $html .= '<td width="100px" align="center">';
-        $html .= '<button onclick="M.tool_spamcleaner.del_user(this,'.$user->id.')">'.get_string('deleteuser', 'admin').'</button><br />';
-        $html .= '<button onclick="M.tool_spamcleaner.ignore_user(this,'.$user->id.')">'.get_string('ignore', 'admin').'</button>';
+        $html .= '<button class="btn btn-primary" onclick="M.tool_spamcleaner.del_user(this,'.$user->id.')">'.
+            get_string('deleteuser', 'admin').'</button><br />';
+        $html .= '<button class="btn btn-secondary" onclick="M.tool_spamcleaner.ignore_user(this,'.$user->id.')">'.
+            get_string('ignore', 'admin').'</button>';
         $html .= '</td>';
         $html .= '</tr>';
         return $html;
diff --git a/comment/index.php b/comment/index.php
index 06bb7da65c4..c6e1a4233da 100644
--- a/comment/index.php
+++ b/comment/index.php
@@ -88,7 +88,8 @@ if (empty($action)) {
     $return = $manager->print_comments($page);
     // if no comments available, $return will be false
     if ($return) {
-        echo '<input type="submit" id="comments_delete" name="batchdelete" value="'.get_string('delete').'" />';
+        echo '<input type="submit" class="btn btn-primary" id="comments_delete" name="batchdelete"
+            value="'.get_string('delete').'" />';
     }
     echo '</form>';
 }
diff --git a/comment/locallib.php b/comment/locallib.php
index a42d2b0f3ff..ec0633e3e2d 100644
--- a/comment/locallib.php
+++ b/comment/locallib.php
@@ -157,7 +157,8 @@ class comment_manager {
 
         $table = new html_table();
         $table->head = array (
-            html_writer::checkbox('selectall', '', false, get_string('selectall'), array('id'=>'comment_select_all', 'class'=>'comment-report-selectall')),
+            html_writer::checkbox('selectall', '', false, get_string('selectall'), array('id' => 'comment_select_all',
+                'class' => 'm-r-1')),
             get_string('author', 'search'),
             get_string('content'),
             get_string('action')
diff --git a/lib/outputcomponents.php b/lib/outputcomponents.php
index 09eb0bdac1f..e7f6bb16ca5 100644
--- a/lib/outputcomponents.php
+++ b/lib/outputcomponents.php
@@ -1680,7 +1680,7 @@ class html_writer {
             $class = str_replace(']', '', $class);
             $attributes['class'] = $class;
         }
-        $attributes['class'] = 'select ' . $attributes['class']; // Add 'select' selector always
+        $attributes['class'] = 'select custom-select ' . $attributes['class']; // Add 'select' selector always.
 
         $attributes['name'] = $name;
 
diff --git a/report/completion/index.php b/report/completion/index.php
index b9f34a4a6cf..20de8a7294c 100644
--- a/report/completion/index.php
+++ b/report/completion/index.php
@@ -311,7 +311,8 @@ if (!$csv) {
         exit;
     }
 
-    print '<table id="completion-progress" class="generaltable flexible boxaligncenter completionreport" style="text-align: left" cellpadding="5" border="1">';
+    print '<table id="completion-progress" class="table table-bordered generaltable flexible boxaligncenter
+        completionreport" style="text-align: left" cellpadding="5" border="1">';
 
     // Print criteria group names
     print PHP_EOL.'<thead><tr style="vertical-align: top">';
diff --git a/report/courseoverview/index.php b/report/courseoverview/index.php
index 8e3d78bf2a7..316a2d87048 100644
--- a/report/courseoverview/index.php
+++ b/report/courseoverview/index.php
@@ -70,7 +70,7 @@ if (empty($timeoptions)) {
     print_error('nostatstodisplay', 'error', $CFG->wwwroot.'/course/view.php?id='.$course->id);
 }
 
-echo html_writer::start_tag('form', array('action' => 'index.php', 'method' => 'post'));
+echo html_writer::start_tag('form', array('action' => 'index.php', 'method' => 'post', 'class' => 'form-inline'));
 echo html_writer::start_tag('div');
 
 $table = new html_table();
@@ -85,8 +85,11 @@ $timeoptionsmenu .= html_writer::select($timeoptions,'time',$time, false);
 $table->data[] = array(get_string('statsreporttype'),$reporttypemenu,
                        get_string('statstimeperiod'),$timeoptionsmenu,
                        html_writer::label(get_string('numberofcourses'), 'numcourses', false, array('class' => 'accesshide')) .
-                       html_writer::empty_tag('input', array('type' => 'text', 'id' => 'numcourses', 'name' => 'numcourses', 'size' => '3', 'maxlength' => '2', 'value' => $numcourses)),
-                       html_writer::empty_tag('input', array('type' => 'submit', 'value' => get_string('view'))));
+                       html_writer::empty_tag('input', array('type' => 'text', 'class' => 'form-control',
+                           'id' => 'numcourses', 'name' => 'numcourses', 'size' => '3', 'maxlength' => '2',
+                           'value' => $numcourses)),
+                       html_writer::empty_tag('input', array('type' => 'submit', 'class' => 'btn btn-secondary',
+                           'value' => get_string('view'))));
 
 echo html_writer::table($table);
 echo html_writer::end_tag('div');
diff --git a/report/log/classes/renderer.php b/report/log/classes/renderer.php
index dc7cbea2cc0..aa93b0731f1 100644
--- a/report/log/classes/renderer.php
+++ b/report/log/classes/renderer.php
@@ -147,7 +147,9 @@ class report_log_renderer extends plugin_renderer_base {
                 'id' => $selectedcourseid, 'date' => $reportlog->date, 'modid' => $reportlog->modid,
                 'showusers' => 1, 'showcourses' => $reportlog->showcourses));
             $a->url = $a->url->out(false);
+            echo html_writer::start_span('m-x-1');
             print_string('logtoomanyusers', 'moodle', $a);
+            echo html_writer::end_span();
         }
 
         // Add date selector.
@@ -186,7 +188,8 @@ class report_log_renderer extends plugin_renderer_base {
                         array('class' => 'accesshide'));
                 echo html_writer::select($readers, 'logreader', $reportlog->selectedlogreader, false);
             }
-            echo html_writer::empty_tag('input', array('type' => 'submit', 'value' => get_string('gettheselogs')));
+            echo html_writer::empty_tag('input', array('type' => 'submit', 'value' => get_string('gettheselogs'),
+                'class' => 'btn btn-secondary'));
         }
         echo html_writer::end_div();
         echo html_writer::end_tag('form');
diff --git a/report/loglive/classes/renderer.php b/report/loglive/classes/renderer.php
index c65e78e72cf..e92a2473aa5 100644
--- a/report/loglive/classes/renderer.php
+++ b/report/loglive/classes/renderer.php
@@ -90,7 +90,8 @@ class report_loglive_renderer extends plugin_renderer_base {
     public function toggle_liveupdate_button(report_loglive_renderable $reportloglive) {
         // Add live log controls.
         if ($reportloglive->page == 0 && $reportloglive->selectedlogreader) {
-            echo html_writer::tag('button' , get_string('pause', 'report_loglive'), array('id' => 'livelogs-pause-button'));
+            echo html_writer::tag('button' , get_string('pause', 'report_loglive'),
+                array('id' => 'livelogs-pause-button', 'class' => 'btn btn-secondary'));
             $icon = new pix_icon('i/loading_small', 'loading', 'moodle', array('class' => 'spinner'));
             return html_writer::tag('span', $this->output->render($icon), array('class' => 'spinner'));
         }
diff --git a/report/participation/index.php b/report/participation/index.php
index 77f75957b0f..964a1690c03 100644
--- a/report/participation/index.php
+++ b/report/participation/index.php
@@ -370,19 +370,20 @@ if (!empty($instanceid) && !empty($roleid)) {
     }
 
     if (!empty($CFG->messaging)) {
-        echo '<div class="selectbuttons">';
-        echo '<input type="button" id="checkall" value="'.get_string('selectall').'" /> '."\n";
-        echo '<input type="button" id="checknone" value="'.get_string('deselectall').'" /> '."\n";
+        $buttonclasses = 'btn btn-secondary';
+        echo '<div class="selectbuttons btn-group">';
+        echo '<input type="button" id="checkall" value="'.get_string('selectall').'" class="'. $buttonclasses .'"> '."\n";
+        echo '<input type="button" id="checknone" value="'.get_string('deselectall').'" class="'. $buttonclasses .'"> '."\n";
         if ($perpage >= $matchcount) {
-            echo '<input type="button" id="checknos" value="'.get_string('selectnos').'" />'."\n";
+            echo '<input type="button" id="checknos" value="'.get_string('selectnos').'" class="'. $buttonclasses .'">'."\n";
         }
         echo '</div>';
-        echo '<div>';
+        echo '<div class="p-y-1">';
         echo html_writer::label(get_string('withselectedusers'), 'formactionselect');
         $displaylist['messageselect.php'] = get_string('messageselectadd');
         echo html_writer::select($displaylist, 'formaction', '', array('' => 'choosedots'), array('id' => 'formactionselect'));
         echo $OUTPUT->help_icon('withselectedusers');
-        echo '<input type="submit" value="' . get_string('ok') . '" />'."\n";
+        echo '<input type="submit" value="' . get_string('ok') . '" class="'. $buttonclasses .'"/>'."\n";
         echo '</div>';
         echo '</div>'."\n";
         echo '</form>'."\n";
diff --git a/report/participation/locallib.php b/report/participation/locallib.php
index 49bbfe5f0e8..f6eeac6c79a 100644
--- a/report/participation/locallib.php
+++ b/report/participation/locallib.php
@@ -220,7 +220,7 @@ function report_participation_print_filter_form($course, $timefrom, $minlog, $ac
         $instanceoptions[] = array(get_string('modulenameplural', $module->name)=>$instances);
     }
 
-    echo '<form class="participationselectform" action="index.php" method="get"><div>'."\n".
+    echo '<form class="participationselectform form-inline" action="index.php" method="get"><div>'."\n".
         '<input type="hidden" name="id" value="'.$course->id.'" />'."\n";
     echo '<label for="menuinstanceid">'.get_string('activitymodule').'</label>'."\n";
     echo html_writer::select($instanceoptions, 'instanceid', $instanceid);
@@ -229,6 +229,6 @@ function report_participation_print_filter_form($course, $timefrom, $minlog, $ac
     echo '<label for="menuroleid">'.get_string('showonly').'</label>'."\n";
     echo html_writer::select($roleoptions,'roleid',$roleid,false);
     echo '<label for="menuaction">'.get_string('showactions').'</label>'."\n";
-    echo html_writer::select($actionoptions,'action',$action,false);
-    echo '<input type="submit" value="'.get_string('go').'" />'."\n</div></form>\n";
+    echo html_writer::select($actionoptions, 'action', $action, false, ['class' => 'm-r-1']);
+    echo '<input type="submit" value="'.get_string('go').'" class="btn btn-primary"/>'."\n</div></form>\n";
 }
diff --git a/report/participation/styles.css b/report/participation/styles.css
index c36366bb8c8..90e3cf84ac5 100644
--- a/report/participation/styles.css
+++ b/report/participation/styles.css
@@ -6,3 +6,8 @@
     margin-left: 15px;
     margin-right: 5px;
 }
+
+/* Die to css conflicts with form-inline, we have to create a specific class to fix submit button alignment on clean */
+#page-report-participation-index .participationselectform input[type="submit"] {
+    margin-bottom: 0;
+}
diff --git a/report/questioninstances/index.php b/report/questioninstances/index.php
index 91c14e112df..33e42376281 100644
--- a/report/questioninstances/index.php
+++ b/report/questioninstances/index.php
@@ -52,7 +52,7 @@ echo '<p id="intro">', get_string('intro', 'report_questioninstances') , '</p>';
 echo '<p><label for="menuqtype"> ' . get_string('questiontype', 'admin') . '</label> ';
 echo html_writer::select($qtypechoices, 'qtype', $requestedqtype, array('_all_'=>get_string('all')));
 echo '</p>';
-echo '<p><input type="submit" id="settingssubmit" value="' .
+echo '<p><input type="submit" class="btn btn-secondary" id="settingssubmit" value="' .
         get_string('getreport', 'report_questioninstances') . '" /></p>';
 echo '</div></form>';
 echo $OUTPUT->box_end();
diff --git a/report/stats/locallib.php b/report/stats/locallib.php
index dafb3716f51..1d2dbd72c62 100644
--- a/report/stats/locallib.php
+++ b/report/stats/locallib.php
@@ -138,18 +138,18 @@ function report_stats_report($course, $report, $mode, $user, $roleid, $time) {
                                html_writer::label(get_string('users'), 'menuuserid'), html_writer::select($users, 'userid', $userid, false),
                                html_writer::label(get_string('statsreporttype'), 'menureport'), html_writer::select($reportoptions, 'report', ($report == 5) ? $report.$roleid : $report, false),
                                html_writer::label(get_string('statstimeperiod'), 'menutime'), html_writer::select($timeoptions, 'time', $time, false),
-                               '<input type="submit" value="'.get_string('view').'" />') ;
+                               '<input type="submit" class="btn btn-secondary" value="'.get_string('view').'" />');
     } else if ($mode == STATS_MODE_RANKED) {
         $table->align = array('left','left','left','left','left','left');
         $table->data[] = array(html_writer::label(get_string('statsreporttype'), 'menureport'), html_writer::select($reportoptions, 'report', ($report == 5) ? $report.$roleid : $report, false),
                                html_writer::label(get_string('statstimeperiod'), 'menutime'), html_writer::select($timeoptions, 'time', $time, false),
-                               '<input type="submit" value="'.get_string('view').'" />') ;
+                               '<input type="submit" class="btn btn-secondary" value="'.get_string('view').'" />');
     } else if ($mode == STATS_MODE_GENERAL) {
         $table->align = array('left','left','left','left','left','left','left');
         $table->data[] = array(html_writer::label(get_string('course'), 'menucourse'), html_writer::select($courseoptions, 'course', $course->id, false),
                                html_writer::label(get_string('statsreporttype'), 'menureport'), html_writer::select($reportoptions, 'report', ($report == 5) ? $report.$roleid : $report, false),
                                html_writer::label(get_string('statstimeperiod'), 'menutime'), html_writer::select($timeoptions, 'time', $time, false),
-                               '<input type="submit" value="'.get_string('view').'" />') ;
+                               '<input type="submit" class="btn btn-secondary" value="'.get_string('view').'" />');
     }
 
     echo '<form action="index.php" method="post">'."\n"
diff --git a/theme/bootstrapbase/less/moodle/admin.less b/theme/bootstrapbase/less/moodle/admin.less
index 0b31b18eb78..872d3742646 100644
--- a/theme/bootstrapbase/less/moodle/admin.less
+++ b/theme/bootstrapbase/less/moodle/admin.less
@@ -155,7 +155,9 @@ img.iconsmall {
     margin-left: auto;
     margin-right: auto;
 }
-
+#page-admin-tool-spamcleaner-index .spamcleanerform input[type="submit"] {
+    margin-bottom: 0;
+}
 .path-admin-roles .capabilitysearchui input[type="button"] {
     margin-bottom: 0;
 }
diff --git a/theme/bootstrapbase/style/moodle.css b/theme/bootstrapbase/style/moodle.css
index 23db2896205..c576b55216f 100644
--- a/theme/bootstrapbase/style/moodle.css
+++ b/theme/bootstrapbase/style/moodle.css
@@ -2751,6 +2751,9 @@ img.iconsmall {
   margin-left: auto;
   margin-right: auto;
 }
+#page-admin-tool-spamcleaner-index .spamcleanerform input[type="submit"] {
+  margin-bottom: 0;
+}
 .path-admin-roles .capabilitysearchui input[type="button"] {
   margin-bottom: 0;
 }