framework/less/lib/FormControl.less

.FormControl {
  display: block;
  width: 100%;
  height: 36px;
  padding: 8px 13px;
  font-size: 13px;
  line-height: 1.5;
  color: @control-color;
  background-color: @control-bg;
  border: 2px solid transparent;
  border-radius: @border-radius;
  .transition(~"border-color .15s, background .15s");
  -webkit-appearance: none;

  &:focus,
  &.focus {
    background-color: @body-bg;
    color: @text-color;
    border-color: @primary-color;
    outline: none;
  }

  // Placeholder
  .placeholder(@control-color);

  // Disabled and read-only inputs
  &[disabled],
  &[readonly],
  fieldset[disabled] & {
    // background-color: @input-bg-disabled;
    opacity: 1; // iOS fix for unreadable disabled content; see https://github.com/twbs/bootstrap/issues/11655
  }

  &[disabled],
  fieldset[disabled] & {
    cursor: disallowed;
  }

  textarea& {
    height: auto;
  }
}
.helpText {
  font-size: 12px;
  line-height: 1.5em;
  margin-bottom: 10px;
  color: @muted-color;
}