diff --git a/theme/boost/scss/moodle/undo.scss b/theme/boost/scss/moodle/undo.scss
index d62ef62bf5f..0ab15fa91c1 100644
--- a/theme/boost/scss/moodle/undo.scss
+++ b/theme/boost/scss/moodle/undo.scss
@@ -192,63 +192,67 @@ body:not(.jsenabled) .langmenu:hover > .dropdown-menu,
  * - Make the content region flex grow so it pushes things like the
  *   next activity selector to the bottom of the page.
  */
-body.reset-style {
-    #page-header {
-        .card {
-            border: none;
+$allow-reset-style: true !default;
 
-            .page-header-headings {
-                h1 {
-                    margin-bottom: 0;
-                }
-            }
-        }
-
-        & > div {
-            padding-top: 0 !important;  /* stylelint-disable-line declaration-no-important */
-            padding-bottom: 0 !important;  /* stylelint-disable-line declaration-no-important */
-        }
-    }
-
-    #page-content {
-        padding-bottom: 0 !important;  /* stylelint-disable-line declaration-no-important */
-
-        #region-main-box {
-            display: flex;
-
-            #region-main {
+@if $allow-reset-style {
+    body.reset-style {
+        #page-header {
+            .card {
                 border: none;
-                display: flex;
-                flex-direction: column;
-                padding: 0;
-                height: 100%;
-                width: 100%;
-                padding-left: $card-spacer-x;
-                padding-right: $card-spacer-x;
 
-                div[role="main"] {
-                    flex: 1;
-                }
-
-                .activity-navigation {
-                    overflow: hidden;
-                }
-
-                &.has-blocks {
-                    width: calc(100% - #{$blocks-plus-gutter});
-
-                    @include media-breakpoint-down(lg) {
-                        width: 100%;
+                .page-header-headings {
+                    h1 {
+                        margin-bottom: 0;
                     }
                 }
             }
 
-            [data-region="blocks-column"] {
-                margin-left: auto;
+            & > div {
+                padding-top: 0 !important;  /* stylelint-disable-line declaration-no-important */
+                padding-bottom: 0 !important;  /* stylelint-disable-line declaration-no-important */
             }
+        }
 
-            @include media-breakpoint-down(lg) {
-                flex-direction: column;
+        #page-content {
+            padding-bottom: 0 !important;  /* stylelint-disable-line declaration-no-important */
+
+            #region-main-box {
+                display: flex;
+
+                #region-main {
+                    border: none;
+                    display: flex;
+                    flex-direction: column;
+                    padding: 0;
+                    height: 100%;
+                    width: 100%;
+                    padding-left: $card-spacer-x;
+                    padding-right: $card-spacer-x;
+
+                    div[role="main"] {
+                        flex: 1;
+                    }
+
+                    .activity-navigation {
+                        overflow: hidden;
+                    }
+
+                    &.has-blocks {
+                        width: calc(100% - #{$blocks-plus-gutter});
+
+                        @include media-breakpoint-down(lg) {
+                            width: 100%;
+                        }
+                    }
+                }
+
+                [data-region="blocks-column"] {
+                    margin-left: auto;
+                }
+
+                @include media-breakpoint-down(lg) {
+                    flex-direction: column;
+                }
             }
         }
     }
diff --git a/theme/classic/scss/classic/pre.scss b/theme/classic/scss/classic/pre.scss
index 258cb4829d2..22736f5cdc3 100644
--- a/theme/classic/scss/classic/pre.scss
+++ b/theme/classic/scss/classic/pre.scss
@@ -1 +1,4 @@
 // General variables for all presets
+
+// Disable the Boost theme reset styling and fixed width content.
+$allow-reset-style: false;
diff --git a/theme/classic/style/moodle.css b/theme/classic/style/moodle.css
index 530800d9afe..9dcb35eada0 100644
--- a/theme/classic/style/moodle.css
+++ b/theme/classic/style/moodle.css
@@ -17619,46 +17619,6 @@ body:not(.jsenabled) .langmenu:hover > .dropdown-menu,
  * - Make the content region flex grow so it pushes things like the
  *   next activity selector to the bottom of the page.
  */
-body.reset-style #page-header .card, body.reset-style #page-header #page-enrol-users #filterform, #page-enrol-users body.reset-style #page-header #filterform, body.reset-style #page-header .que .history, .que body.reset-style #page-header .history, body.reset-style #page-header .userprofile .profile_tree section, .userprofile .profile_tree body.reset-style #page-header section, body.reset-style #page-header .groupinfobox, body.reset-style #page-header .well {
-  border: none; }
-  body.reset-style #page-header .card .page-header-headings h1, body.reset-style #page-header #page-enrol-users #filterform .page-header-headings h1, #page-enrol-users body.reset-style #page-header #filterform .page-header-headings h1, body.reset-style #page-header .que .history .page-header-headings h1, .que body.reset-style #page-header .history .page-header-headings h1, body.reset-style #page-header .userprofile .profile_tree section .page-header-headings h1, .userprofile .profile_tree body.reset-style #page-header section .page-header-headings h1, body.reset-style #page-header .groupinfobox .page-header-headings h1, body.reset-style #page-header .well .page-header-headings h1 {
-    margin-bottom: 0; }
-
-body.reset-style #page-header > div {
-  padding-top: 0 !important;
-  /* stylelint-disable-line declaration-no-important */
-  padding-bottom: 0 !important;
-  /* stylelint-disable-line declaration-no-important */ }
-
-body.reset-style #page-content {
-  padding-bottom: 0 !important;
-  /* stylelint-disable-line declaration-no-important */ }
-  body.reset-style #page-content #region-main-box {
-    display: flex; }
-    body.reset-style #page-content #region-main-box #region-main {
-      border: none;
-      display: flex;
-      flex-direction: column;
-      padding: 0;
-      height: 100%;
-      width: 100%;
-      padding-left: 1.25rem;
-      padding-right: 1.25rem; }
-      body.reset-style #page-content #region-main-box #region-main div[role="main"] {
-        flex: 1; }
-      body.reset-style #page-content #region-main-box #region-main .activity-navigation {
-        overflow: hidden; }
-      body.reset-style #page-content #region-main-box #region-main.has-blocks {
-        width: calc(100% - 375px); }
-        @media (max-width: 1199.98px) {
-          body.reset-style #page-content #region-main-box #region-main.has-blocks {
-            width: 100%; } }
-    body.reset-style #page-content #region-main-box [data-region="blocks-column"] {
-      margin-left: auto; }
-    @media (max-width: 1199.98px) {
-      body.reset-style #page-content #region-main-box {
-        flex-direction: column; } }
-
 body.behat-site .fixed-top {
   position: absolute; }