mdb-ui-kit/scss/_forms.scss

// label variations
.label {
  border-radius: $border-radius-small;
  //@include variations(unquote(""), background-color, $grey);
}

// must be broken out for reuse - webkit selector breaks firefox
@mixin label-static($label-top, $static-font-size, $static-line-height) {
  label.control-label {
    top: $label-top;
    left: 0;
    // must repeat because the selector above is more specific than the general label sizing
    //font-size: $static-font-size;
    //line-height: $static-line-height;
  }
}

@mixin label-size-variant($placeholder-font-size, $vertical-padding, $line-height, $static-font-size, $static-line-height, $help-block-font-size) {
  .form-control {
    @include material-placeholder {
      //font-size: $placeholder-font-size;
      //line-height: $line-height;
      //color: $mdb-input-placeholder-color;
      //font-weight: 400;
    }

    // margin-bottom must be specified to give help-block vertical space.
    //    $see also form-group padding-bottom (and size variants) re: collapsible margins.  These work together.
    //margin-bottom: $vertical-padding;
  }

  // generic labels used anywhere in the form (not control-label)
  .checkbox label,
  .radio label,
  label {
    //font-size: $placeholder-font-size;
    //line-height: $line-height;
    //color: $mdb-input-placeholder-color;
    //font-weight: 400;
  }

  // smaller focused or static size
  label.control-label {
    //font-size: $static-font-size;
    //line-height: $static-line-height;
    //color: $mdb-input-placeholder-color;
    //font-weight: 400;
    //margin: 16px 0 0 0; // std and lg
  }

  .help-block {
    //margin-top: 0; // allow the input margin to set-off the top of the help-block
    //font-size: $help-block-font-size;
  }
}

@mixin mdb-form-group-validation-state($name, $color) {

  &.has-#{$name} { // e.g. has-error
    .form-control {
      //box-shadow: none; // replaced with variable
    }

    // e.g. form-control-success
    .form-control-#{$name} {
      //  background-image: none;
    }

    &.is-focused {
      .form-control {
        //background-image: linear-gradient($color, $color), linear-gradient($mdb-input-underline-color, $mdb-input-underline-color);
      }
      .mdb-form-control-decorator::after {
        //background-color: $color;
      }
      label.control-label,
      .help-block {
        color: $color;
      }
    }
  }
}

@mixin mdb-form-group-size-variant($parent, $placeholder-font-size, $label-top-margin, $vertical-padding, $line-height, $label-as-placeholder-shim) {
  $static-font-size: ceil(($mdb-label-static-size-ratio * $placeholder-font-size)) !default;
  $static-line-height: ($mdb-label-static-size-ratio * $line-height) !default;

  $label-as-placeholder-top: -1 * ($vertical-padding + $label-as-placeholder-shim) !default;
  $label-top: $label-as-placeholder-top - ($placeholder-font-size + $vertical-padding) !default;

  $help-block-font-size: ceil(($mdb-help-block-size-ratio * $placeholder-font-size)) !default;
  $help-block-line-height: ($mdb-help-block-size-ratio * $line-height) !default;

  // this is outside a form-group
  @if not $parent {
    @include label-size-variant($placeholder-font-size, $vertical-padding, $line-height, $static-font-size, $static-line-height, $help-block-font-size);
  } @else {
    // this is inside a form-group, may be .mdb-form-group.mdb-form-group-sm or .mdb-form-group.mdb-form-group-lg
    #{$parent} {
      @include label-size-variant($placeholder-font-size, $vertical-padding, $line-height, $static-font-size, $static-line-height, $help-block-font-size);

      // form-group padding-bottom
      //  upon collapsing margins, the largest margin is honored which collapses the form-control margin-bottom,
      //  so the form-control margin-bottom must also be expressed as form-group padding
      //padding-bottom: $vertical-padding;

      // FIXME: need to avoid top margin http://v4-alpha.getbootstrap.com/content/reboot/#approach
      // form-group margin-top must be large enough for the label and the label's top padding since label is absolutely positioned
      //margin: ($label-top-margin + $static-font-size) 0 0 0; // old, try padding below
      //padding-top: ($label-top-margin + $static-font-size);

      // larger labels as placeholders
      &.label-floating,
      &.label-placeholder {
        label.control-label {
          top: $label-as-placeholder-top; // place the floating label to look like a placeholder with input padding
          //font-size: $placeholder-font-size;
          //line-height: $line-height;
        }
      }

      // static, focused, or autofill floating labels
      &.label-static,
      &.label-floating.is-focused,
      &.label-floating:not(.is-empty) {
        @include label-static($label-top, $static-font-size, $static-line-height);
      }
      // #559 Fix for webkit/chrome autofill - rule must be separate because it breaks firefox otherwise #731
      &.label-floating input.form-control:-webkit-autofill ~ label.control-label {
        @include label-static($label-top, $static-font-size, $static-line-height);
      }
    }
  }
}

// -----
// Inputs
//
// Reference http://www.google.com/design/spec/components/text-fields.html
// MDL implementation: http://www.getmdl.io/components/index.html#textfields-section
//.mdb-form-group .form-control,
.form-control {
  //background-image: linear-gradient($brand-primary, $brand-primary), linear-gradient($mdb-input-underline-color, $mdb-input-underline-color);
  //background-repeat: no-repeat;
  //background-position: center bottom, center calc(100% - 1px);
  //background-size: 0 2px, 100% 1px;
  //transition: background 0s ease-out;

  //float: none;  // why?

  // The border bottom should be static in all states, the decorator will be animated over this.
  &,
  &:focus,
  .mdb-form-group.is-focused & {
    border: 0;
    border-bottom: $input-border-width solid $input-border-color;
  }

  &[disabled],
  fieldset[disabled] & {
    //background-image: none;
    border-bottom: $input-border-width dotted $input-border-color;
  }

  //&:textarea {
  //  height: 40px;
  //}

  //&:focus,
  //.mdb-form-group.is-focused & {
  //  background-size: 100% 2px, 100% 1px;
  //  outline: none; // redundant - in bootstrap
  //  transition-duration: 0.3s;
  //}
  //.mdb-form-group.is-focused .mdb-form-control-decorator::after {
  //  background-color: $brand-primary;
  //}

  //&[readonly],
  //&[disabled],
  //fieldset[disabled] & {
  //  background-color: rgba($black, 0);  // replaced with $input-bg-disabled
  //}
}

// Focus underline animation =================================
.mdb-form-control-decorator {
  position: relative;
  top: (-1 * $input-border-width); // move the top up enough to overlay the border from the input
  display: block;
  &::before,
  &::after {
    position: absolute;
    width: 0;
    height: $input-border-width;
    content: "";
    @include gradient-vertical($brand-primary, $mdb-input-underline-color);
    transition: 0.3s ease all;

    // focused state - it transitions the width of each (before and after) to 50% creating the center out effect
    .form-control:focus ~ &,
    .mdb-form-group.is-focused .form-control ~ & {
      width: 50%;
    }
  }
  &::before {
    left: 50%;
  }
  &::after {
    right: 50%;
  }
}
// Focus underline animation =================================

// -----
// Labels with mdb-form-group signalled state
//
// Reference http://www.google.com/design/spec/components/text-fields.html
// MDL implementation: http://www.getmdl.io/components/index.html#textfields-section
//.variations(unquote(" label.control-label"), color, $mdb-input-placeholder-color);  // default label color variations

.mdb-form-group {
  position: relative;

  // -----
  // Labels with form-group signalled state
  //
  // Reference http://www.google.com/design/spec/components/text-fields.html
  // MDL implementation: http://www.getmdl.io/components/index.html#textfields-section
  &.label-static,
  &.label-placeholder,
  &.label-floating {
    label.control-label {
      //position: absolute;
      //pointer-events: none;
      //transition: 0.3s ease all;
    }
  }

  // hint to browser for optimization
  //    TODO: evaluate effectiveness - looking for community feedback
  &.label-floating label.control-label {
    //will-change: left, top, contents;
  }

  // hide label-placeholders when the field is not empty
  &.label-placeholder:not(.is-empty) {
    label.control-label {
      display: none;
    }
  }

  // Help blocks - position: absolute approach - uses no vertical space, text wrapping - not so good.
  .help-block {
    //position: absolute; // do not use position: absolute because width/wrapping isn't automatic and overflows occur
    //display: none;
  }

  // form-group is-focused display
  &.is-focused {

    label,
    label.control-label {
      color: $brand-primary;
    }

    &.label-placeholder {
      label,
      label.control-label {
        //color: $mdb-input-placeholder-color;
      }
    }

    .help-block {
      //display: block;
    }
  }

  @include mdb-form-group-validation-state(warning, $brand-warning);
  @include mdb-form-group-validation-state(error, $brand-danger);
  @include mdb-form-group-validation-state(success, $brand-success);
  @include mdb-form-group-validation-state(info, $brand-info);

  textarea {
    //resize: none;
    ~ .form-control-highlight {
      //margin-top: -11px;
    }
  }

  select {
    //appearance: none; // Fix for OS X

    ~ .mdb-form-control-decorator::after {
      //display: none;
    }
  }
}

// default floating size/location without a form-group (will skip form-group styles, and just render default sizing variation)
@include mdb-form-group-size-variant(null, $font-size-base, $mdb-label-top-margin-base, $mdb-input-padding-y-base, $line-height, $mdb-label-as-placeholder-shim-base);

// default floating size/location with a form-group (need margin etc from a default form-group)
@include mdb-form-group-size-variant(unquote(".mdb-form-group"), $font-size-base, $mdb-label-top-margin-base, $mdb-input-padding-y-base, $line-height, $mdb-label-as-placeholder-shim-base);

// sm floating size/location
@include mdb-form-group-size-variant(unquote(".mdb-form-group.mdb-form-group-sm"), $font-size-sm, $mdb-label-top-margin-sm, $mdb-input-padding-y-sm, $line-height-sm, $mdb-label-as-placeholder-shim-sm);

// lg floating size/location
@include mdb-form-group-size-variant(unquote(".mdb-form-group.mdb-form-group-lg"), $font-size-lg, $mdb-label-top-margin-lg, $mdb-input-padding-y-lg, $line-height-lg, $mdb-label-as-placeholder-shim-lg);

select.form-control {
  //border: 0;
  //box-shadow: none;
  //border-radius: 0;

  .mdb-form-group.is-focused & {
    //box-shadow: none;
    //border-color: $mdb-input-underline-color;
  }

  &[multiple] {
    &,
    .mdb-form-group.is-focused & {
      //height: 85px;
    }
  }
}

// Input files - hide actual input - requires specific markup in the sample.
//.mdb-form-group input[type=file] {
//  opacity: 0;
//  position: absolute;
//  top: 0;
//  right: 0;
//  bottom: 0;
//  left: 0;
//  width: 100%;
//  height: 100%;
//  z-index: 100;
//}

//  I don't think this was in use...
//legend {
//  border-bottom: 0;
//}
//
//
//.form-horizontal {
//
//  // Consistent vertical alignment of radios and checkboxes
//  .radio,
//  .checkbox,
//  .radio-inline,
//  .checkbox-inline {
//    padding-top: 0;
//  }
//
//  .radio {
//    margin-bottom: 10px;
//  }
//
//  label {
//    text-align: right;
//  }
//
//  label.control-label {
//    margin: 0;
//  }
//}