ten-design-vue/lib/theme/mixins/form.less

ten-vue

.placeholder(@color: @placeholder-color) {
  // Firefox
  &::-moz-placeholder {
    color: @color;
    opacity: 1; // Override Firefox's unusual default opacity; see https://github.com/twbs/bootstrap/pull/11526
  }
  // Internet Explorer 10+
  &:-ms-input-placeholder {
    color: @color;
  }
  // Safari and Chrome
  &::-webkit-input-placeholder {
    color: @color;
  }
}