Drop IE support from Sass

scss/_card.scss

@@ -132,7 +132,6 @@
 .card-img,
 .card-img-top,
 .card-img-bottom {
-  flex-shrink: 0; // For IE: https://github.com/twbs/bootstrap/issues/29396
   width: 100%; // Required because we use flexbox and this inherently applies align-self: stretch
 }
 

scss/_modal.scss

@@ -56,11 +56,9 @@
 }
 
 .modal-dialog-scrollable {
-  display: flex; // IE10/11
   max-height: subtract(100%, $modal-dialog-margin * 2);
 
   .modal-content {
-    max-height: subtract(100vh, $modal-dialog-margin * 2); // IE10/11
     overflow: hidden;
   }
 
@@ -78,29 +76,6 @@
   display: flex;
   align-items: center;
   min-height: subtract(100%, $modal-dialog-margin * 2);
-
-  // Ensure `modal-dialog-centered` extends the full height of the view (IE10/11)
-  &::before {
-    display: block; // IE10
-    height: subtract(100vh, $modal-dialog-margin * 2);
-    height: min-content; // Reset height to 0 except on IE
-    content: "";
-  }
-
-  // Ensure `.modal-body` shows scrollbar (IE10/11)
-  &.modal-dialog-scrollable {
-    flex-direction: column;
-    justify-content: center;
-    height: 100%;
-
-    .modal-content {
-      max-height: none;
-    }
-
-    &::before {
-      content: none;
-    }
-  }
 }
 
 // Actual modal

scss/_navbar.scss

@@ -107,10 +107,10 @@
 // the default flexbox row orientation. Requires the use of `flex-wrap: wrap`
 // on the `.navbar` parent.
 .navbar-collapse {
-  flex: 1 0 100%;
   // For always expanded or extra full navbars, ensure content aligns itself
   // properly vertically. Can be easily overridden with flex utilities.
   align-items: center;
+  width: 100%;
 }
 
 // Button for toggling the navbar when in its collapsed state
@@ -173,9 +173,6 @@
 
         .navbar-collapse {
           display: flex !important; // stylelint-disable-line declaration-no-important
-
-          // Changes flex-bases to auto because of an IE10 bug
-          flex-basis: auto;
         }
 
         .navbar-toggler {

scss/_reboot.scss

@@ -34,7 +34,7 @@
 //
 // 1. Remove the margin in all browsers.
 // 2. As a best practice, apply a default `background-color`.
-// 3. Prevent adjustments of font size after orientation changes in IE on Windows Phone and in iOS.
+// 3. Prevent adjustments of font size after orientation changes in iOS.
 // 4. Change the default tap highlight to be completely transparent in iOS.
 
 body {
@@ -145,7 +145,7 @@ p {
 // Abbreviations
 //
 // 1. Duplicate behavior to the data-* attribute for our tooltip plugin
-// 2. Add the correct text decoration in Chrome, Edge, IE, Opera, and Safari.
+// 2. Add the correct text decoration in Chrome, Edge, Opera, and Safari.
 // 3. Add explicit cursor to indicate changed behavior.
 // 4. Prevent the text-decoration to be skipped.
 
@@ -344,15 +344,8 @@ figure {
 
 // Images and content
 
-img {
-  vertical-align: middle;
-}
-
-// 1. Workaround for the SVG overflow bug in IE 11 is still required.
-//    See https://github.com/twbs/bootstrap/issues/26878
-
+img,
 svg {
-  overflow: hidden; // 1
   vertical-align: middle;
 }
 
@@ -399,7 +392,7 @@ button {
   border-radius: 0;
 }
 
-// Work around a Firefox/IE bug where the transparent `button` background
+// Work around a Firefox bug where the transparent `button` background
 // results in a loss of the default `button` focus styles.
 // Credit https://github.com/suitcss/base/
 
@@ -487,12 +480,10 @@ input[type="month"] {
   -webkit-appearance: textfield;
 }
 
-// 1. Remove the default vertical scrollbar in IE.
-// 2. Textareas should really only resize vertically so they don't break their (horizontal) containers.
+// 1. Textareas should really only resize vertically so they don't break their (horizontal) containers.
 
 textarea {
-  overflow: auto; // 1
-  resize: vertical; // 2
+  resize: vertical; // 1
 }
 
 // 1. Browsers set a default `min-width: min-content;` on fieldsets,
@@ -510,8 +501,7 @@ fieldset {
 }
 
 // 1. By using `float: left`, the legend will behave like a block element
-// 2. Correct the color inheritance from `fieldset` elements in IE.
-// 3. Correct the text wrapping in Edge and IE.
+// 2. Correct the text wrapping in Edge.
 
 legend {
   float: left; // 1
@@ -521,8 +511,7 @@ legend {
   @include font-size($legend-font-size);
   font-weight: $legend-font-weight;
   line-height: inherit;
-  color: inherit; // 2
-  white-space: normal; // 3
+  white-space: normal; // 2
 }
 
 // Fix height of inputs with a type of datetime-local, date, month, week, or time
@@ -581,22 +570,6 @@ summary {
 }
 
 
-// Template
-//
-// Add the correct display for template & main in IE 11
-
-template {
-  display: none;
-}
-
-
-// Main
-
-main {
-  display: block;
-}
-
-
 // Progress
 //
 // Add the correct vertical alignment in Chrome, Firefox, and Opera.

scss/_variables.scss

@@ -720,7 +720,7 @@ $form-range-thumb-border:                  0 !default;
 $form-range-thumb-border-radius:           1rem !default;
 $form-range-thumb-box-shadow:              0 .1rem .25rem rgba($black, .1) !default;
 $form-range-thumb-focus-box-shadow:        0 0 0 1px $body-bg, $input-focus-box-shadow !default;
-$form-range-thumb-focus-box-shadow-width:  $input-focus-width !default; // For focus box shadow issue in IE/Edge
+$form-range-thumb-focus-box-shadow-width:  $input-focus-width !default; // For focus box shadow issue in Edge
 $form-range-thumb-active-bg:               lighten($component-active-bg, 35%) !default;
 $form-range-thumb-disabled-bg:             $gray-500 !default;
 $form-range-thumb-transition:              background-color .15s ease-in-out, border-color .15s ease-in-out, box-shadow .15s ease-in-out !default;

scss/forms/_form-select.scss

@@ -37,7 +37,7 @@
       // For visual consistency with other platforms/browsers,
       // suppress the default white text on blue background highlight given to
       // the selected option text when the (still closed) <select> receives focus
-      // in IE and (under certain conditions) Edge.
+      // in Edge.
       // See https://github.com/twbs/bootstrap/issues/19398.
       color: $input-color;
       background-color: $input-bg;