diff --git a/Gruntfile.js b/Gruntfile.js
index 08b28b675ff..7622be1ec8d 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -185,11 +185,6 @@ module.exports = function(grunt) {
                     configOverrides: {
                         rules: {
                             // TODO: MDL-55165 -Enable these rules once we make output-changing changes to less.
-                            "declaration-block-no-ignored-properties": null,
-                            "value-keyword-case": null,
-                            "declaration-block-no-duplicate-properties": null,
-                            "declaration-block-no-shorthand-property-overrides": null,
-                            "selector-type-no-unknown": null,
                             "length-zero-no-unit": null,
                             "color-hex-case": null,
                             "color-hex-length": null,
diff --git a/theme/bootstrapbase/less/moodle/admin.less b/theme/bootstrapbase/less/moodle/admin.less
index 40d36391dd3..3b7eb534c0f 100644
--- a/theme/bootstrapbase/less/moodle/admin.less
+++ b/theme/bootstrapbase/less/moodle/admin.less
@@ -406,7 +406,6 @@ img.iconsmall {
 }
 
 .form-item .form-setting .form-htmlarea {
-    width: 640px;
     display: inline;
 }
 
diff --git a/theme/bootstrapbase/less/moodle/core.less b/theme/bootstrapbase/less/moodle/core.less
index e8fa7ed33e6..91745b473a7 100644
--- a/theme/bootstrapbase/less/moodle/core.less
+++ b/theme/bootstrapbase/less/moodle/core.less
@@ -1132,8 +1132,6 @@ tr.flagged-tag a {
             display: inline;
             float: none;
             clear: none;
-            width: auto;
-            margin: 0;
         }
         select,
         .ftext input {
@@ -1409,7 +1407,6 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
     filter: 0;
 }
 .moodle-dialogue-base .moodle-dialogue-wrap .moodle-dialogue-hd h1 {
-    margin: 0;
     padding: 0;
     display: inline;
     font-size: 100%;
@@ -1422,7 +1419,6 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
     width: 25px;
     height: 15px;
     float: right;
-    vertical-align: middle;
     display: inline-block;
     cursor: pointer;
     padding: 0;
@@ -1725,7 +1721,7 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
     padding: 3px 7px;
     font-size: 12px;
     font-weight: bold;
-    background-color: whiteSmoke;
+    background-color: #f5f5f5;
     border: 1px solid #ddd;
     color: #9DA0A4;
     .border-radius(4px 0 4px 0);
@@ -1955,7 +1951,6 @@ img#persona_signin {
 }
 .invisiblefieldset {
     display: inline;
-    margin: 0;
     padding: 0;
     border-width: 0;
 }
diff --git a/theme/bootstrapbase/less/moodle/course.less b/theme/bootstrapbase/less/moodle/course.less
index c47254a24d6..c2af4daf7ae 100644
--- a/theme/bootstrapbase/less/moodle/course.less
+++ b/theme/bootstrapbase/less/moodle/course.less
@@ -51,7 +51,6 @@
         .spinner {
             left: 100%;
             position: absolute;
-            vertical-align: text-bottom;
         }
 
         .editing_move {
@@ -862,7 +861,6 @@ span.editinstructions {
 
     .item-actions {
         margin-right: 1em;
-        display: inline-block;
         display: initial;
         > a img,
         .menubar img {
@@ -1081,7 +1079,6 @@ span.editinstructions {
         float: right;
         line-height: 40px;
         > div {
-            margin-left: 1em;
             margin: 10px 0;
             display: inline-block;
         }
diff --git a/theme/bootstrapbase/less/moodle/filemanager.less b/theme/bootstrapbase/less/moodle/filemanager.less
index 908c85ca138..13d742a0c0c 100644
--- a/theme/bootstrapbase/less/moodle/filemanager.less
+++ b/theme/bootstrapbase/less/moodle/filemanager.less
@@ -195,7 +195,7 @@
     border-radius: 4px;
     background: white;
 }
-.fp-repo-items fp-viewbar {
+.fp-repo-items .fp-viewbar {
     margin: 4px;
 }
 
diff --git a/theme/bootstrapbase/less/moodle/forms.less b/theme/bootstrapbase/less/moodle/forms.less
index 9d0e8c6a6da..381f7f94682 100644
--- a/theme/bootstrapbase/less/moodle/forms.less
+++ b/theme/bootstrapbase/less/moodle/forms.less
@@ -101,7 +101,6 @@ form {
 .mform fieldset.fdate_selector label {
     display: inline;
     float: none;
-    width: auto;
 }
 .mform .ftags label.accesshide {
     display: block;
diff --git a/theme/bootstrapbase/less/moodle/question.less b/theme/bootstrapbase/less/moodle/question.less
index e5c304917a5..e024786ae64 100644
--- a/theme/bootstrapbase/less/moodle/question.less
+++ b/theme/bootstrapbase/less/moodle/question.less
@@ -116,7 +116,6 @@
     overflow-y: auto;
     padding: 1.5em 1.6em;
     background-color: #fff;
-    overflow-y: auto;
 }
 #chooseqtype .instruction,
 #chooseqtype .selected .qtypesummary {
@@ -179,7 +178,6 @@
 }
 body.path-question-type .fitem_fgroup .accesshide {
     font: inherit;
-    left: 0;
     position: static;
     padding-right: .3em;
 }
@@ -379,7 +377,6 @@ body.path-question-type .fitem_fgroup .accesshide {
 #page-mod-quiz-edit .questionbankwindow div.header {
     color: #444;
     text-shadow: none;
-    padding: 3px;
     .border-top-radius(4px);
     margin: 0 -10px 0 -10px;
     padding: 2px 10px 2px 10px;
diff --git a/theme/bootstrapbase/less/moodle/reports.less b/theme/bootstrapbase/less/moodle/reports.less
index b27a058406b..4f6b0fb7891 100644
--- a/theme/bootstrapbase/less/moodle/reports.less
+++ b/theme/bootstrapbase/less/moodle/reports.less
@@ -5,7 +5,7 @@
 // and replace it completely.
 
 #page-report-participation-index .participationselectform div label { // Using 'div' here to override the report styles.css
-    display: inline;
+    display: inline-block;
     margin: 0 5px; // No top and bottom margin with a 5px left and right for LTR and RTL.
 }
 
diff --git a/theme/bootstrapbase/less/moodle/responsive.less b/theme/bootstrapbase/less/moodle/responsive.less
index e30817ba2db..796ed053d5e 100644
--- a/theme/bootstrapbase/less/moodle/responsive.less
+++ b/theme/bootstrapbase/less/moodle/responsive.less
@@ -226,7 +226,6 @@
     }
     .fp-content-center {
         display: block;
-        vertical-align: top;
     }
     .course-content ul.topics li.section,
     .course-content ul.topics li.section .content,
diff --git a/theme/bootstrapbase/less/moodle/undo.less b/theme/bootstrapbase/less/moodle/undo.less
index 31704bf388c..ec72d9ae6ec 100644
--- a/theme/bootstrapbase/less/moodle/undo.less
+++ b/theme/bootstrapbase/less/moodle/undo.less
@@ -121,7 +121,6 @@ div.c1.btn {
     font-size: inherit;
     line-height: inherit;
     text-align: inherit;
-    vertical-align: inherit;
     cursor: default;
     color: inherit;
     text-shadow: inherit;