// 可替代 transition 使用
transition($op = all, $time = 0.28s, $ease = ease-out)
  transition: $op $time $ease
  -moz-transition: $op $time $ease
  -webkit-transition: $op $time $ease
  -o-transition: $op $time $ease

// 为1个属性设置动画
trans1($op, $time = 0.2s)
  transition: $op $time ease-out
  -moz-transition: $op $time ease-out
  -webkit-transition: $op $time ease-out
  -o-transition: $op $time ease-out

// 为2个属性设置动画
trans2($op1, $op2)
  transition: $op1 0.2s ease-out, $op2 0.2s ease-out
  -moz-transition: $op1 0.2s ease-out, $op2 0.2s ease-out
  -webkit-transition: $op1 0.2s ease-out, $op2 0.2s ease-out
  -o-transition: $op1 0.2s ease-out, $op2 0.2s ease-out


txt-ellipsis()
  white-space: nowrap
  overflow: hidden
  text-overflow: ellipsis

placeholder(rules)
  &::-webkit-input-placeholder
    rules()
  &:-moz-placeholder
    rules()
	&::-moz-placeholder
    rules()
	&:-ms-input-placeholder
    rules()

disable-select()
  -moz-user-select: none
  -ms-user-select: none
  -webkit-user-select: none
  user-select: none