diff --git a/Gruntfile.js b/Gruntfile.js
index 7622be1ec8d..f09f5f7a870 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -185,7 +185,6 @@ module.exports = function(grunt) {
                     configOverrides: {
                         rules: {
                             // TODO: MDL-55165 -Enable these rules once we make output-changing changes to less.
-                            "length-zero-no-unit": null,
                             "color-hex-case": null,
                             "color-hex-length": null,
                             // These rules have to be disabled in .stylelintrc for scss compat.
diff --git a/theme/bootstrapbase/less/moodle/admin.less b/theme/bootstrapbase/less/moodle/admin.less
index 3b7eb534c0f..192d2cb253f 100644
--- a/theme/bootstrapbase/less/moodle/admin.less
+++ b/theme/bootstrapbase/less/moodle/admin.less
@@ -650,7 +650,7 @@ img.iconsmall {
 
         .status {
             .actionbutton {
-                margin: 5px 0px;
+                margin: 5px 0;
                 padding: 0;
                 input {
                     margin: 0;
diff --git a/theme/bootstrapbase/less/moodle/blocks.less b/theme/bootstrapbase/less/moodle/blocks.less
index e58df2671c6..69f1b19f5a7 100644
--- a/theme/bootstrapbase/less/moodle/blocks.less
+++ b/theme/bootstrapbase/less/moodle/blocks.less
@@ -158,7 +158,7 @@
         .footer {
             margin-top: .5em;
             padding-top: 10px;
-            padding-left: 0px;
+            padding-left: 0;
         }
     }
 }
@@ -204,7 +204,7 @@
     }
     .footer {
         padding-top: 10px;
-        padding-left: 0px;
+        padding-left: 0;
     }
 }
 
diff --git a/theme/bootstrapbase/less/moodle/calendar.less b/theme/bootstrapbase/less/moodle/calendar.less
index f010ee8b96c..96579af231e 100644
--- a/theme/bootstrapbase/less/moodle/calendar.less
+++ b/theme/bootstrapbase/less/moodle/calendar.less
@@ -362,7 +362,7 @@
     font-size: 10px;
     font-weight: bold;
     background-color: #f60;
-    padding: 0px 5px;
+    padding: 0 5px;
     color: #fff;
     border-top: 1px solid #f93;
     border-left: 1px solid #f93;
diff --git a/theme/bootstrapbase/less/moodle/core.less b/theme/bootstrapbase/less/moodle/core.less
index 91745b473a7..605ce7c2730 100644
--- a/theme/bootstrapbase/less/moodle/core.less
+++ b/theme/bootstrapbase/less/moodle/core.less
@@ -721,12 +721,12 @@ img.user-image {
 .path-tag .tag-index-items .tagarea h3 {
     display: block;
     padding: 3px 0 10px 0;
-    margin: 0px;
+    margin: 0;
     font-size: 1.1em;
     font-weight: bold;
     line-height: 20px;
     color: #999;
-    text-shadow: 0px 1px 0px rgba(255, 255, 255, 0.5);
+    text-shadow: 0 1px 0 rgba(255, 255, 255, 0.5);
     text-transform: uppercase;
     word-wrap: break-word;
     border-bottom: solid 1px #E3E3E3;
@@ -842,7 +842,7 @@ tr.flagged-tag a {
     text-align: center;
 }
 .tag_cloud .inline-list li {
-    padding: 0px 0.2em;
+    padding: 0 0.2em;
 }
 .tag_cloud .tag_overflow {
     margin-top: 1em;
@@ -1360,9 +1360,9 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
     overflow: hidden;
 }
 .moodle-dialogue-base .moodle-dialogue-fullscreen {
-    left: 0px;
-    top: 0px;
-    right: 0px;
+    left: 0;
+    top: 0;
+    right: 0;
     bottom: -50px;
     position: fixed;
 }
@@ -1445,16 +1445,16 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
 .moodle-dialogue-base .moodle-dialogue-fullscreen .moodle-dialogue-content {
     overflow: auto;
     position: absolute;
-    top: 0px;
+    top: 0;
     bottom: 50px;
-    left: 0px;
-    right: 0px;
-    margin: 0px;
-    border: 0px;
+    left: 0;
+    right: 0;
+    margin: 0;
+    border: 0;
 }
 .moodle-dialogue-base .moodle-dialogue-fullscreen .moodle-dialogue-hd,
 .moodle-dialogue-base .moodle-dialogue-fullscreen .moodle-dialogue-wrap {
-    border-radius: 0px;
+    border-radius: 0;
 }
 .moodle-dialogue-confirm .confirmation-dialogue {
     text-align: center;
@@ -1603,7 +1603,7 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
     overflow-x: hidden;
     overflow-y: auto;
     max-width: 20.3em;
-    .box-shadow(inset 0 0 30px 0px #ccc);
+    .box-shadow(inset 0 0 30px 0 #ccc);
     .option {
         input[type=radio] {
             display: inline-block;
@@ -1790,12 +1790,12 @@ table.collection .actions {
 }
 
 a.criteria-action {
-    padding: 0px 3px;
+    padding: 0 3px;
     float: right;
 }
 div.criteria-description {
     padding: 10px 15px;
-    margin: 5px 0px;
+    margin: 5px 0;
     background: none repeat scroll 0 0 #f9f9f9;
     border: 1px solid #EEE;
 }
@@ -1822,7 +1822,7 @@ ul.badges {
     width: 100px;
     height: 100px;
     left: 10px;
-    top: 0px;
+    top: 0;
     z-index: 1;
 }
 .badges li .badge-actions {
@@ -1832,7 +1832,7 @@ ul.badges {
     width: 100px;
     height: 100px;
     left: 25px;
-    top: 0px;
+    top: 0;
     position: absolute;
     z-index: 10;
     opacity: 0.85;
@@ -1851,8 +1851,8 @@ ul.badges {
     .expireimage {
         width: 100px;
         height: 100px;
-        left: 0px;
-        top: 0px;
+        left: 0;
+        top: 0;
         .opacity(85);
         position: absolute;
         z-index: 10;
@@ -1862,7 +1862,7 @@ ul.badges {
         padding-top: 5px;
 
         input {
-            margin-left: 0px;
+            margin-left: 0;
         }
     }
 }
@@ -1939,7 +1939,7 @@ ul.badges {
     margin: 3px;
 }
 .activatebadge {
-    margin: 0px;
+    margin: 0;
     text-align: left;
     vertical-align: middle;
 }
@@ -2064,8 +2064,8 @@ img#persona_signin {
 
             .iconsmall,
             .smallicon {
-                margin: 4px 4px 4px 0px;
-                padding: 8px 4px 0px 2px;
+                margin: 4px 4px 4px 0;
+                padding: 8px 4px 0 2px;
                 vertical-align: text-bottom;
             }
 
diff --git a/theme/bootstrapbase/less/moodle/course.less b/theme/bootstrapbase/less/moodle/course.less
index c2af4daf7ae..9811c8fdaa2 100644
--- a/theme/bootstrapbase/less/moodle/course.less
+++ b/theme/bootstrapbase/less/moodle/course.less
@@ -684,8 +684,8 @@ span.editinstructions {
         .iconsmall {
             width: 12px;
             height: 12px;
-            margin: 8px 8px 0px 0;
-            padding: 4px 8px 0px 0;
+            margin: 8px 8px 0 0;
+            padding: 4px 8px 0 0;
             vertical-align: text-bottom;
         }
     }
diff --git a/theme/bootstrapbase/less/moodle/filemanager.less b/theme/bootstrapbase/less/moodle/filemanager.less
index 13d742a0c0c..807ebf1dd2c 100644
--- a/theme/bootstrapbase/less/moodle/filemanager.less
+++ b/theme/bootstrapbase/less/moodle/filemanager.less
@@ -77,7 +77,7 @@
 }
 
 .moodle-dialogue-base .filepicker .moodle-dialogue-wrap .moodle-dialogue-bd {
-    padding: 0px;
+    padding: 0;
 }
 
 // File Picker layout
@@ -103,8 +103,8 @@
     margin-left: 181px;
 }
 .moodle-dialogue-fullscreen .file-picker .fp-repo-items {
-    margin-left: 0px;
-    margin-right: 0px;
+    margin-left: 0;
+    margin-right: 0;
     float: left;
 }
 .file-picker .fp-navbar {
@@ -282,7 +282,7 @@
 .fp-iconview .fp-thumbnail:hover {
     background: #fff;
     border: 1px solid #ddd;
-    .box-shadow(inset 0 0 10px 0px #ccc);
+    .box-shadow(inset 0 0 10px 0 #ccc);
 }
 .fp-iconview .fp-filename-field {
     height: 33px;
diff --git a/theme/bootstrapbase/less/moodle/forms.less b/theme/bootstrapbase/less/moodle/forms.less
index 381f7f94682..3087c476dd9 100644
--- a/theme/bootstrapbase/less/moodle/forms.less
+++ b/theme/bootstrapbase/less/moodle/forms.less
@@ -374,7 +374,7 @@ fieldset.coursesearchbox label {
         margin-bottom: 4px;
     }
     .availability-plugincontrols {
-        padding: 2px 0px 0px 4px;
+        padding: 2px 0 0 4px;
         background: none repeat scroll 0% 0% @wellBackground;
         border: 1px solid @grayLighter;
         border-radius: 4px;
@@ -420,6 +420,7 @@ fieldset.coursesearchbox label {
     }
 }
 
+
 /* Default form styling colours all text red. With availability conditions
    this looks excessive as we show 'Invalid' markers in specific places. */
 .mform .error .availability-field {
@@ -487,8 +488,8 @@ input[size] {
     min-width: 206px;
     max-height: 20em;
     overflow: auto;
-    margin: 0px;
-    padding: 0px;
+    margin: 0;
+    padding: 0;
     margin-top: -0.2em;
     z-index: 1;
 }
diff --git a/theme/bootstrapbase/less/moodle/grade.less b/theme/bootstrapbase/less/moodle/grade.less
index 1679fbce8e6..bb80f7afcd5 100644
--- a/theme/bootstrapbase/less/moodle/grade.less
+++ b/theme/bootstrapbase/less/moodle/grade.less
@@ -92,14 +92,14 @@
                     vertical-align: top;
                     padding: @rubricPadding;
                     textarea {
-                        margin-bottom: 0px;
+                        margin-bottom: 0;
                         height: 115px;
                     }
                 }
                 .definition {
                     textarea {
                         width: 80%;
-                        margin-bottom: 0px;
+                        margin-bottom: 0;
                     }
                 }
                 .score {
@@ -107,7 +107,7 @@
                     float: left;
                     margin-right: 28px;
                     input {
-                        margin-bottom: 0px;
+                        margin-bottom: 0;
                     }
                 }
                 .level {
@@ -127,7 +127,7 @@
                             bottom: 0;
                             height: 24px;
                             width: 24px;
-                            margin: 0px;
+                            margin: 0;
                             &:hover {
                                 background-color: #ddd;
                             }
@@ -151,7 +151,7 @@
                     vertical-align: middle;
                     input {
                         .btn();
-                        background-position: 0px 0px;
+                        background-position: 0 0;
                         height: 30px;
                         margin-right: 5px;
                     }
@@ -166,7 +166,7 @@
                 margin: 0;
                 color: inherit;
                 text-shadow: inherit;
-                border: 0px none;
+                border: 0 none;
                 line-height: inherit;
                 background: transparent url([[pix:t/add]]) no-repeat 7px 8px;
                 padding-left: 26px;
diff --git a/theme/bootstrapbase/less/moodle/modules.less b/theme/bootstrapbase/less/moodle/modules.less
index 345e3583d89..3514265a174 100644
--- a/theme/bootstrapbase/less/moodle/modules.less
+++ b/theme/bootstrapbase/less/moodle/modules.less
@@ -611,7 +611,7 @@ div#dock {
                 &:hover img {
                     background: #fff;
                     border-radius: 4px;
-                    box-shadow: 0px 0px 16px rgba(0, 0, 0, 0.125);
+                    box-shadow: 0 0 16px rgba(0, 0, 0, 0.125);
                 }
             }
         }
@@ -682,7 +682,7 @@ div#dock {
                     &:hover img {
                         background: #333;
                         border-radius: 4px;
-                        box-shadow: 0px 0px 16px rgba(255, 255, 255, 1);
+                        box-shadow: 0 0 16px rgba(255, 255, 255, 1);
                     }
                 }
             }
@@ -721,7 +721,7 @@ div#dock {
 
             > .menubar {
                 display: block;
-                margin: 0px;
+                margin: 0;
             }
             > .menu {
                 min-width: 160px;
@@ -877,7 +877,7 @@ div#dock {
     }
 
     .qnbutton.flagged .thispageholder {
-        background: transparent url([[pix:theme|mod/quiz/flag-on]]) 15px 0px no-repeat;
+        background: transparent url([[pix:theme|mod/quiz/flag-on]]) 15px 0 no-repeat;
     }
 
     .qnbutton .trafficlight {
diff --git a/theme/bootstrapbase/less/moodle/question.less b/theme/bootstrapbase/less/moodle/question.less
index e024786ae64..9f30c659eba 100644
--- a/theme/bootstrapbase/less/moodle/question.less
+++ b/theme/bootstrapbase/less/moodle/question.less
@@ -135,7 +135,7 @@
         padding-left: 5px;
     }
     .checkbox input[type="checkbox"] {
-        margin-left: 0px;
+        margin-left: 0;
         float: none;
     }
     img.iconsmall {
@@ -438,7 +438,7 @@ body.path-question-type .fitem_fgroup .accesshide {
 }
 #page-mod-quiz-edit div.question div.content div.points {
     margin-top: -0.5em;
-    padding-bottom: 0em;
+    padding-bottom: 0;
     border: none;
     background-color: @bodyBackground;
     position: static;
diff --git a/theme/bootstrapbase/less/moodle/responsive.less b/theme/bootstrapbase/less/moodle/responsive.less
index 796ed053d5e..0525f9d15da 100644
--- a/theme/bootstrapbase/less/moodle/responsive.less
+++ b/theme/bootstrapbase/less/moodle/responsive.less
@@ -52,7 +52,7 @@
         height: auto;
         max-height: 220px;
         float: none;
-        border: 0px;
+        border: 0;
     }
     .file-picker .fp-repo-items {
         width: 100%;
diff --git a/theme/bootstrapbase/less/moodle/undo.less b/theme/bootstrapbase/less/moodle/undo.less
index ec72d9ae6ec..b9e28136e4b 100644
--- a/theme/bootstrapbase/less/moodle/undo.less
+++ b/theme/bootstrapbase/less/moodle/undo.less
@@ -162,8 +162,8 @@ img.icon-pre {
 .loginbox.twocolumns {
     .signuppanel,
     .loginpanel {
-        padding: 0px;
-        margin: 0px;
+        padding: 0;
+        margin: 0;
     }
 }