Merge branch 'v4-dev' into btn_input_split_variables

diff --cc scss/_button-group.scss
Simple merge

diff --cc scss/_buttons.scss
Simple merge

diff --cc scss/_forms.scss
index 5ac3f88a2f77c362485199317a8d1d847cbe7a40,42f2399e87019377ff61f166d85423bcd94386a8..d2a1b3601d86bc6593884cc7720e4f62c18206d0
--- 1/scss/_forms.scss
--- 2/scss/_forms.scss
+++ b/scss/_forms.scss
@@@ -7,15 -7,13 +7,13 @@@
  .form-control {
    display: block;
    width: 100%;
 -  padding: $input-btn-padding-y $input-btn-padding-x;
 +  padding: $input-padding-y $input-padding-x;
    font-size: $font-size-base;
 -  line-height: $input-btn-line-height;
 +  line-height: $input-line-height;
    color: $input-color;
    background-color: $input-bg;
-   // Reset unusual Firefox-on-Android default style; see https://github.com/necolas/normalize.css/issues/214.
-   background-image: none;
    background-clip: padding-box;
 -  border: $input-btn-border-width solid $input-border-color;
 +  border: $input-border-width solid $input-border-color;
  
    // Note: This has no effect on <select>s in some browsers, due to the limited stylability of `<select>`s in CSS.
    @if $enable-rounded {
@@@ -129,13 -127,15 +127,15 @@@ select.form-control 
  // text (without any border, background color, focus indicator)
  
  .form-control-plaintext {
 -  padding-top: $input-btn-padding-y;
 -  padding-bottom: $input-btn-padding-y;
+   display: block;
+   width: 100%;
 +  padding-top: $input-padding-y;
 +  padding-bottom: $input-padding-y;
    margin-bottom: 0; // match inputs if this class comes on inputs with default margins
 -  line-height: $input-btn-line-height;
 +  line-height: $input-line-height;
    background-color: transparent;
    border: solid transparent;
 -  border-width: $input-btn-border-width 0;
 +  border-width: $input-border-width 0;
  
    &.form-control-sm,
    &.form-control-lg {

diff --cc scss/_input-group.scss
index f5eed46f9f82cb35da3602d6f68ac67e4a68c0a1,ae70ebc081ebf9fcc55f796a479b57580a7e1826..771fd6ec869c784f87be7e0a2714e8b5b8cae97e
--- 1/scss/_input-group.scss
--- 2/scss/_input-group.scss
+++ b/scss/_input-group.scss
@@@ -168,8 -168,8 +168,8 @@@
    &:not(:first-child) {
      > .btn,
      > .btn-group {
-       z-index: 2;
+       z-index: 1;
 -      // remove nagative margin ($input-btn-border-width) to solve overlapping issue with button.
 +      // remove nagative margin ($input-border-width) to solve overlapping issue with button.
        margin-left: 0;
  
        // When input is first, overlap the right side of it with the button(-group)

diff --cc scss/_variables.scss
index f141994df5c7ee89dbf56ca137edd3aee91a6284,50972c53b9bd9aa746816079ac4744d141914e42..2ea031c15748ea06091cbc55896234760eb42423
--- 1/scss/_variables.scss
--- 2/scss/_variables.scss
+++ b/scss/_variables.scss
@@@ -320,31 -330,9 +328,30 @@@ $input-btn-padding-y-lg:      .5rem !de
  $input-btn-padding-x-lg:      1rem !default;
  $input-btn-line-height-lg:    $line-height-lg !default;
  
 +$input-btn-border-width:      $border-width !default; // For form controls and buttons
 +
 +
 +// Buttons
 +//
 +// For each of Bootstrap's buttons, define text, background and border color.
 +
 +$btn-padding-y:               $input-btn-padding-y !default;
 +$btn-padding-x:               $input-btn-padding-x !default;
 +$btn-line-height:             $input-btn-line-height !default;
 +
 +$btn-padding-y-sm:            $input-btn-padding-y-sm !default;
 +$btn-padding-x-sm:            $input-btn-padding-x-sm !default;
 +$btn-line-height-sm:          $input-btn-line-height-sm !default;
 +
 +$btn-padding-y-lg:            $input-btn-padding-y-lg !default;
 +$btn-padding-x-lg:            $input-btn-padding-x-lg !default;
 +$btn-line-height-lg:          $input-btn-line-height-lg !default;
 +
 +$btn-border-width:            $input-btn-border-width !default;
 +
  $btn-font-weight:             $font-weight-normal !default;
- $btn-box-shadow:              inset 0 1px 0 rgba($white,.15), 0 1px 1px rgba($black,.075) !default;
- $btn-focus-box-shadow:        0 0 0 3px rgba(theme-color("primary"), .25) !default;
- $btn-active-box-shadow:       inset 0 3px 5px rgba($black,.125) !default;
+ $btn-box-shadow:              inset 0 1px 0 rgba($white, .15), 0 1px 1px rgba($black, .075) !default;
+ $btn-active-box-shadow:       inset 0 3px 5px rgba($black, .125) !default;
  
  $btn-link-disabled-color:     $gray-600 !default;