Remove IE9 browser hacks. (#21393)

scss/_custom-forms.scss

@@ -131,8 +131,6 @@
 // Replaces the browser default select with a custom one, mostly pulled from
 // http://primercss.io.
 //
-// Includes hacks for IE9 (noted by ` \9`), which may apply to other versions of
-// IE, but not with any adverse affects.
 
 .custom-select {
   display: inline-block;
@@ -140,11 +138,9 @@
   $select-border-width: ($border-width * 2);
   height: calc(#{$input-height} - #{$select-border-width});
   padding: $custom-select-padding-y ($custom-select-padding-x + $custom-select-indicator-padding) $custom-select-padding-y $custom-select-padding-x;
-  padding-right: $custom-select-padding-x \9;
   color: $custom-select-color;
   vertical-align: middle;
   background: $custom-select-bg $custom-select-indicator no-repeat right $custom-select-padding-x center;
-  background-image: none \9;
   background-size: $custom-select-bg-size;
   border: $custom-select-border-width solid $custom-select-border-color;
   @include border-radius($custom-select-border-radius);

scss/_dropdown.scss

@@ -105,7 +105,6 @@
       cursor: $cursor-disabled;
       background-color: transparent;
       background-image: none; // Remove CSS gradient
-      @include reset-filter();
     }
   }
 }

scss/_mixins.scss

@@ -23,7 +23,6 @@
 @import "mixins/hover";
 @import "mixins/image";
 @import "mixins/badge";
-@import "mixins/reset-filter";
 @import "mixins/resize";
 @import "mixins/screen-reader";
 @import "mixins/size";

scss/_progress.scss

@@ -54,21 +54,6 @@ base::-moz-progress-bar, // Absurd-but-syntactically-valid selector to make thes
   @include box-shadow($progress-box-shadow);
 }
 
-// IE9 hacks to accompany custom markup. We don't need to scope this via media queries, but I feel better doing it anyway.
-@media screen and (min-width:0\0) {
-  .progress {
-    background-color: $progress-bg;
-    @include border-radius($progress-border-radius);
-    @include box-shadow($progress-box-shadow);
-  }
-  .progress-bar {
-    display: inline-block;
-    height: $spacer-y;
-    text-indent: -999rem; // Simulate hiding of value as in native `<progress>`
-    background-color: $progress-bar-color;
-  }
-}
-
 
 //
 // Striped
@@ -86,13 +71,6 @@ base::-moz-progress-bar, // Absurd-but-syntactically-valid selector to make thes
   @include gradient-striped();
   background-size: $spacer-y $spacer-y;
 }
-// IE9
-@media screen and (min-width:0\0) {
-  .progress-bar-striped {
-    @include gradient-striped();
-    background-size: $spacer-y $spacer-y;
-  }
-}
 
 
 //
@@ -105,12 +83,6 @@ base::-moz-progress-bar, // Absurd-but-syntactically-valid selector to make thes
 .progress-animated[value]::-moz-progress-bar {
   animation: progress-bar-stripes 2s linear infinite;
 }
-// IE9
-@media screen and (min-width:0\0) {
-  .progress-animated .progress-bar-striped {
-    animation: progress-bar-stripes 2s linear infinite;
-  }
-}
 
 
 //

scss/_tables.scss

@@ -143,7 +143,6 @@
 .table-responsive {
   display: block;
   width: 100%;
-  min-height: 0%; // Workaround for IE9 bug (see https://github.com/twbs/bootstrap/issues/14837)
   overflow-x: auto;
   -ms-overflow-style: -ms-autohiding-scrollbar; // See https://github.com/twbs/bootstrap/pull/10057
 

scss/mixins/_gradients.scss

@@ -3,11 +3,9 @@
 // Horizontal gradient, from left to right
 //
 // Creates two color stops, start and end, by specifying a color and position for each color stop.
-// Color stops are not available in IE9.
 @mixin gradient-x($start-color: #555, $end-color: #333, $start-percent: 0%, $end-percent: 100%) {
   background-image: linear-gradient(to right, $start-color $start-percent, $end-color $end-percent);
   background-repeat: repeat-x;
-  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#{ie-hex-str($start-color)}', endColorstr='#{ie-hex-str($end-color)}', GradientType=1); // IE9
 }
 
 // Vertical gradient, from top to bottom
@@ -17,7 +15,6 @@
 @mixin gradient-y($start-color: #555, $end-color: #333, $start-percent: 0%, $end-percent: 100%) {
   background-image: linear-gradient(to bottom, $start-color $start-percent, $end-color $end-percent);
   background-repeat: repeat-x;
-  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#{ie-hex-str($start-color)}', endColorstr='#{ie-hex-str($end-color)}', GradientType=0); // IE9
 }
 
 @mixin gradient-directional($start-color: #555, $end-color: #333, $deg: 45deg) {
@@ -27,12 +24,10 @@
 @mixin gradient-x-three-colors($start-color: #00b3ee, $mid-color: #7a43b6, $color-stop: 50%, $end-color: #c3325f) {
   background-image: linear-gradient(to right, $start-color, $mid-color $color-stop, $end-color);
   background-repeat: no-repeat;
-  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#{ie-hex-str($start-color)}', endColorstr='#{ie-hex-str($end-color)}', GradientType=1); // IE9 gets no color-stop at all for proper fallback
 }
 @mixin gradient-y-three-colors($start-color: #00b3ee, $mid-color: #7a43b6, $color-stop: 50%, $end-color: #c3325f) {
   background-image: linear-gradient($start-color, $mid-color $color-stop, $end-color);
   background-repeat: no-repeat;
-  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#{ie-hex-str($start-color)}', endColorstr='#{ie-hex-str($end-color)}', GradientType=0); // IE9 gets no color-stop at all for proper fallback
 }
 @mixin gradient-radial($inner-color: #555, $outer-color: #333) {
   background-image: radial-gradient(circle, $inner-color, $outer-color);
@@ -40,4 +35,4 @@
 }
 @mixin gradient-striped($color: rgba(255,255,255,.15), $angle: 45deg) {
   background-image: linear-gradient($angle, $color 25%, transparent 25%, transparent 50%, $color 50%, $color 75%, transparent 75%, transparent);
-}
+}

scss/mixins/_progress.scss

@@ -13,11 +13,4 @@
   &[value]::-ms-fill {
     background-color: $color;
   }
-
-  // IE9
-  @media screen and (min-width:0\0) {
-    .progress-bar {
-      background-color: $color;
-    }
-  }
 }

scss/mixins/_reset-filter.scss

@@ -1,8 +0,0 @@
-// Reset filters for IE
-//
-// When you need to remove a gradient background, do not forget to use this to reset
-// the IE filter for IE9.
-
-@mixin reset-filter() {
-  filter: "progid:DXImageTransform.Microsoft.gradient(enabled = false)";
-}