42  

You could do it like this

你可以这样做

HTML:

HTML：

  
  Your email address

CSS:

CSS：

input:focus ~ .floating-label,
input:not(:focus):valid ~ .floating-label{
  top: 8px;
  bottom: 10px;
  left: 20px;
  font-size: 11px;
  opacity: 1;
}

.inputText {
  font-size: 14px;
  width: 200px;
  height: 35px;
}

.floating-label {
  position: absolute;
  pointer-events: none;
  left: 20px;
  top: 18px;
  transition: 0.2s ease all;
}

Working JSFiddle here https://jsfiddle.net/273ntk5s/2/

在这里工作JSFiddle https://jsfiddle.net/273ntk5s/2/

3  

.user-input-wrp {
	position: relative;
	width: 50%;
}
.user-input-wrp .inputText{
	width: 100%;
	outline: none;
	border:none;
	border-bottom: 1px solid #777;
}
.user-input-wrp .inputText:invalid {
	box-shadow: none !important;
}
.user-input-wrp .inputText:focus{
	border-color: blue;
	border-width: medium medium 2px;
}
.user-input-wrp .floating-label {
	position: absolute;
	pointer-events: none;
	top: 18px;
	left: 10px;
	transition: 0.2s ease all;
}
.user-input-wrp input:focus ~ .floating-label,
.user-input-wrp input:not(:focus):valid ~ .floating-label{
	top: 0px;
	left: 10px;
	font-size: 13px;
	opacity: 1;
}

The floating label

  

  
  Your email address

Modified the code from @user1846747 a little.

稍微修改了@ user1846747的代码。

2  

That site isn't moving the placeholder, but placing a div (.floating-label) over the input, so when the input is focused the div just animates to be over the input. The key part here is using pointer-events: none; in the floating div, so when you click it the event goes through it to the input box behind it.

该站点没有移动占位符，而是在输入上放置div（.floating-label），因此当输入被聚焦时，div只是动画来完成输入。这里的关键部分是使用指针事件：无;在浮动div中，所以当你点击它时，事件会通过它进入它后面的输入框。

1  

span{
  display:block;
  }
input:focus::-webkit-input-placeholder { color:transparent; }
input:focus:-moz-placeholder { color:transparent; } /* FF 4-18 */
input:focus::-moz-placeholder { color:transparent; } /* FF 19+ */
input:focus:-ms-input-placeholder { color:transparent; } /* IE 10+ */