diff --git a/theme/boost/scss/preset/default.scss b/theme/boost/scss/preset/default.scss
index 084598bdb63..414346de8a3 100644
--- a/theme/boost/scss/preset/default.scss
+++ b/theme/boost/scss/preset/default.scss
@@ -2,6 +2,9 @@
 // Bootstrap variables
 //
 
+// Prefix for all CSS variables
+$prefix: bs- !default;
+
 // Colors
 $white:    #fff !default;
 $gray-100: #f8f9fa !default;
@@ -71,7 +74,8 @@ $card-group-margin: .25rem;
 
 // Inputs
 $focus-ring-opacity: .75 !default;
-$input-border-color: $gray-500 !default;
+$input-border-color: var(--#{$prefix}gray-500) !default;
+$form-check-input-border: var(--#{$prefix}border-width) solid var(--#{$prefix}gray-500) !default;
 
 // Dropdowns
 $dropdown-link-hover-color: $white;
diff --git a/theme/boost/style/moodle.css b/theme/boost/style/moodle.css
index 62c10088276..5022efcefbe 100644
--- a/theme/boost/style/moodle.css
+++ b/theme/boost/style/moodle.css
@@ -15459,7 +15459,7 @@ progress {
   appearance: none;
   background-color: var(--bs-body-bg);
   background-clip: padding-box;
-  border: var(--bs-border-width) solid #8f959e;
+  border: var(--bs-border-width) solid var(--bs-gray-500);
   border-radius: var(--bs-border-radius);
   transition: border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out;
 }
@@ -15612,7 +15612,7 @@ textarea.form-control-lg {
   background-repeat: no-repeat;
   background-position: right 0.75rem center;
   background-size: 16px 12px;
-  border: var(--bs-border-width) solid #8f959e;
+  border: var(--bs-border-width) solid var(--bs-gray-500);
   border-radius: var(--bs-border-radius);
   transition: border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out;
 }
@@ -15693,7 +15693,7 @@ textarea.form-control-lg {
   background-repeat: no-repeat;
   background-position: center;
   background-size: contain;
-  border: var(--bs-border-width) solid var(--bs-border-color);
+  border: var(--bs-border-width) solid var(--bs-gray-500);
   print-color-adjust: exact;
 }
 .form-check-input[type=checkbox] {
@@ -15998,7 +15998,7 @@ textarea.form-control-lg {
   text-align: center;
   white-space: nowrap;
   background-color: var(--bs-tertiary-bg);
-  border: var(--bs-border-width) solid #8f959e;
+  border: var(--bs-border-width) solid var(--bs-gray-500);
   border-radius: var(--bs-border-radius);
 }
 
@@ -29308,14 +29308,14 @@ img.icon {
   }
   .admin_colourpicker .colourdialogue {
     float: left;
-    border: 1px solid #8f959e;
+    border: 1px solid var(--bs-gray-500);
   }
   .admin_colourpicker .previewcolour {
-    border: 1px solid #8f959e;
+    border: 1px solid var(--bs-gray-500);
     margin-left: 301px;
   }
   .admin_colourpicker .currentcolour {
-    border: 1px solid #8f959e;
+    border: 1px solid var(--bs-gray-500);
     margin-left: 301px;
     border-top-width: 0;
   }
@@ -32250,7 +32250,7 @@ body.drawer-ease {
 }
 
 .fp-navbar {
-  border-color: #8f959e;
+  border-color: var(--bs-gray-500);
   border-bottom: 0;
   border-bottom-left-radius: 0;
   border-bottom-right-radius: 0;
@@ -32803,7 +32803,7 @@ a.ygtvspacer:hover {
 .filepicker-filelist,
 .filemanager-container {
   min-height: 140px;
-  border: 1px solid #8f959e;
+  border: 1px solid var(--bs-gray-500);
   border-radius: 0.5rem;
 }
 
@@ -34720,7 +34720,7 @@ body.path-question-type .mform fieldset.hidden {
   margin: 0;
 }
 .simplesearchform .btn-submit {
-  border-color: #8f959e;
+  border-color: var(--bs-gray-500);
   color: #6a737b;
 }
 .simplesearchform .btn-close,
@@ -35043,7 +35043,7 @@ div#dateselector-calendar-panel {
 .form-autocomplete-suggestions {
   position: absolute;
   background-color: #fff;
-  border: 1px solid #8f959e;
+  border: 1px solid var(--bs-gray-500);
   min-width: 206px;
   max-height: 20em;
   overflow: auto;
@@ -35729,7 +35729,7 @@ select {
     height: calc(1.5em + 1rem + calc(var(--bs-border-width) * 2));
     border-radius: 0;
     background-color: var(--bs-body-bg);
-    border-color: #8f959e;
+    border-color: var(--bs-gray-500);
     padding-left: calc(0.5rem + 8px);
     padding-top: 0.5rem;
     padding-bottom: 0.5rem;
@@ -35744,7 +35744,7 @@ select {
     height: calc(1.5em + 1rem + calc(var(--bs-border-width) * 2));
     border-radius: 0;
     background-color: var(--bs-body-bg);
-    border-color: #8f959e;
+    border-color: var(--bs-gray-500);
     padding-left: calc(0.5rem + 8px);
     padding-top: 0.5rem;
     padding-bottom: 0.5rem;
@@ -39297,7 +39297,7 @@ div.editor_atto_toolbar {
   display: block;
   background: #f2f2f2;
   min-height: 35px;
-  border: 1px solid #8f959e;
+  border: 1px solid var(--bs-gray-500);
   width: 100%;
   padding: 0 0 9px 0;
   border-top-left-radius: 0.5rem;
diff --git a/theme/classic/scss/preset/default.scss b/theme/classic/scss/preset/default.scss
index f194a6f00e2..637e305b100 100644
--- a/theme/classic/scss/preset/default.scss
+++ b/theme/classic/scss/preset/default.scss
@@ -2,6 +2,9 @@
 // Bootstrap variables
 //
 
+// Prefix for all CSS variables
+$prefix: bs- !default;
+
 // Colors
 $white:    #fff !default;
 $gray-100: #f8f9fa !default;
@@ -49,13 +52,13 @@ $theme-colors: map-merge((
 ), $theme-colors);
 // stylelint-enable
 
-// Tables
-$table-accent-bg: rgba($black, .03) !default;
-
 // Fonts
 $font-size-base: 0.9375rem !default;
 $headings-font-weight:   300 !default;
 
+// Links
+$link-decoration: none !default;
+
 // Navbar
 $navbar-dark-hover-color:           rgba($white, 1) !default;
 $navbar-light-color:                rgba($black, 0.6) !default;
@@ -71,6 +74,7 @@ $card-group-margin: .25rem;
 // Inputs
 $focus-ring-opacity: .75 !default;
 $input-border-color: $gray-500 !default;
+$form-check-input-border: var(--#{$prefix}border-width) solid var(--#{$prefix}gray-500) !default;
 
 // Dropdowns
 $dropdown-link-hover-color: $white;