Bump bootstrap to 4.3.1

style/bootstrap/_close.scss

@@ -1,34 +1,41 @@
-.close {
-  float: right;
-  font-size: $close-font-size;
-  font-weight: $close-font-weight;
-  line-height: 1;
-  color: $close-color;
-  text-shadow: $close-text-shadow;
-  opacity: .5;
-
-  @include hover-focus {
-    color: $close-color;
-    text-decoration: none;
-    opacity: .75;
-  }
-
-  // Opinionated: add "hand" cursor to non-disabled .close elements
-  &:not(:disabled):not(.disabled) {
-    cursor: pointer;
-  }
-}
-
-// Additional properties for button version
-// iOS requires the button element instead of an anchor tag.
-// If you want the anchor version, it requires `href="#"`.
-// See https://developer.mozilla.org/en-US/docs/Web/Events/click#Safari_Mobile
-
-// stylelint-disable property-no-vendor-prefix, selector-no-qualifying-type
-button.close {
-  padding: 0;
-  background-color: transparent;
-  border: 0;
-  -webkit-appearance: none;
-}
-// stylelint-enable
+.close {
+  float: right;
+  @include font-size($close-font-size);
+  font-weight: $close-font-weight;
+  line-height: 1;
+  color: $close-color;
+  text-shadow: $close-text-shadow;
+  opacity: .5;
+
+  // Override <a>'s hover style
+  @include hover {
+    color: $close-color;
+    text-decoration: none;
+  }
+
+  &:not(:disabled):not(.disabled) {
+    @include hover-focus {
+      opacity: .75;
+    }
+  }
+}
+
+// Additional properties for button version
+// iOS requires the button element instead of an anchor tag.
+// If you want the anchor version, it requires `href="#"`.
+// See https://developer.mozilla.org/en-US/docs/Web/Events/click#Safari_Mobile
+
+// stylelint-disable-next-line selector-no-qualifying-type
+button.close {
+  padding: 0;
+  background-color: transparent;
+  border: 0;
+  appearance: none;
+}
+
+// Future-proof disabling of clicks on `<a>` elements
+
+// stylelint-disable-next-line selector-no-qualifying-type
+a.close.disabled {
+  pointer-events: none;
+}