diff --git a/core/scss/mixins/_functions.scss b/core/scss/mixins/_functions.scss
index b276a113a..9176033f1 100644
--- a/core/scss/mixins/_functions.scss
+++ b/core/scss/mixins/_functions.scss
@@ -19,7 +19,7 @@
 // "Bootstrap functions" section below.
 
 @mixin media-breakpoint-down-than($name, $breakpoints: $grid-breakpoints) {
-  $prev: breakpoint-prev($name);
+  $prev: breakpoint-prev($name, $breakpoints);
 
   @if $prev == null {
     @content;
diff --git a/core/scss/mixins/bootstrap/_caret.scss b/core/scss/mixins/bootstrap/_caret.scss
index 7fd6c4df2..3b601e1d5 100644
--- a/core/scss/mixins/bootstrap/_caret.scss
+++ b/core/scss/mixins/bootstrap/_caret.scss
@@ -33,7 +33,7 @@
 @mixin caret($direction: down, $width: $caret-width, $spacing: $caret-spacing, $vertical-align: $caret-vertical-align) {
   $selector: 'after';
 
-  @if $direction == 'left' {
+  @if $direction == 'start' {
     $selector: 'before';
   }
 
@@ -47,7 +47,7 @@
     border-inline-start: 1px var(--border-style);
     margin-inline-end: 0.1em;
 
-    @if $direction != 'left' {
+    @if $direction != 'start' {
       margin-inline-start: $caret-spacing;
     } @else {
       margin-inline-end: $caret-spacing;
@@ -64,7 +64,7 @@
     }
   }
 
-  @if $direction == 'left' {
+  @if $direction == 'start' {
     &::after {
       content: none;
     }
diff --git a/core/scss/tests/_caret.test.scss b/core/scss/tests/_caret.test.scss
index 2fcca4d7f..d5e022b3c 100644
--- a/core/scss/tests/_caret.test.scss
+++ b/core/scss/tests/_caret.test.scss
@@ -1,7 +1,7 @@
 // Output tests for the caret mixins in scss/mixins/bootstrap/_caret.scss.
 // The `caret-{down,up,end,start}` helpers draw a triangle out of borders; the
 // main `caret()` builds a pseudo-element and branches on `$direction` for the
-// rotation and (for `left`) the ::before/::after structure.
+// rotation and (for `start`) the ::before/::after structure.
 
 @use '../mixins/bootstrap/caret' as *;
 
@@ -86,11 +86,11 @@
     }
   }
 
-  @include it('uses ::before and clears ::after for the left direction') {
+  @include it('uses ::before and clears ::after for the start direction') {
     @include assert() {
       @include output() {
         .t {
-          @include caret(left);
+          @include caret(start);
         }
       }
       @include expect() {
diff --git a/core/scss/tests/_media-breakpoint.test.scss b/core/scss/tests/_media-breakpoint.test.scss
index 1412d6315..85ddee4e2 100644
--- a/core/scss/tests/_media-breakpoint.test.scss
+++ b/core/scss/tests/_media-breakpoint.test.scss
@@ -174,4 +174,29 @@ $g: (
       }
     }
   }
+
+  // Names that don't exist in the global $grid-breakpoints at all: this only
+  // resolves if $breakpoints actually reaches the breakpoint-prev() lookup,
+  // not just the breakpoint-max() one.
+  $custom: (
+    tablet: 0,
+    desktop: 900px,
+  );
+
+  @include it('resolves the previous breakpoint from a custom $breakpoints map') {
+    @include assert() {
+      @include output() {
+        @include media-breakpoint-down-than(desktop, $custom) {
+          .t {
+            color: red;
+          }
+        }
+      }
+      @include expect() {
+        .t {
+          color: red;
+        }
+      }
+    }
+  }
 }
diff --git a/core/scss/ui/_type.scss b/core/scss/ui/_type.scss
index 4ba9d86e8..2ef211c2d 100644
--- a/core/scss/ui/_type.scss
+++ b/core/scss/ui/_type.scss
@@ -9,10 +9,10 @@
 
 a {
   text-decoration-skip-ink: auto;
-  color: color-mix(in sRGB, transparent, var(--link-color) var(--link-opacity, 100%));
+  color: color-mix(in sRGB, transparent, var(--link-color) calc(var(--link-opacity, 1) * 100%));
 
   &:hover {
-    color: color-mix(in sRGB, transparent, var(--link-hover-color) var(--link-opacity, 100%));
+    color: color-mix(in sRGB, transparent, var(--link-hover-color) calc(var(--link-opacity, 1) * 100%));
   }
 }