Matching an empty input field using CSS

In modern browsers you can use :placeholder-shown to target the empty input (not to be confused with ::placeholder).

input:placeholder-shown {
    border: 1px solid red; /* Red border only if the input is empty */
}

In HTML you must set the placeholder attribute. Chrome browser requires at least a space character as value.

<input type="text" placeholder=" "> <!-- Do not remove placeholder -->

If only the field is required you could go with input:valid

#foo-thing:valid + .msg { visibility: visible!important; }      

 <input type="text" id="foo-thing" required="required">
 <span class="msg" style="visibility: hidden;">Yay not empty</span>

See live on jsFiddle

OR negate using #foo-thing:invalid (credit to @SamGoody)

input[value=""], input:not([value])

works with:

<input type="text" />
<input type="text" value="" />

But the style will not change as soon as someone will start typing (you need JS for that).

Updating the value of a field does not update its value attribute in the DOM so that's why your selector is always matching a field, even when it's not actually empty.

Instead use the invalid pseudo-class to achieve what you want, like so:

input:required {
  border: 1px solid green;
}
input:required:invalid {
  border: 1px solid red;
}

<input required type="text" value="">

<input required type="text" value="Value">

I realize this is a very old thread, but things have changed a bit since and it did help me find the right combination of things I needed to get my problem fixed. So I thought I'd share what I did.

The problem was I needed to have the same css applied for an optional input if it was filled, as I had for a filled required. The css used the psuedo class :valid which applied the css on the optional input also when not filled.

This is how I fixed it;

HTML

<input type="text" required="required">
<input type="text" placeholder="">

CSS

input:required:valid {
    ....
}
input:optional::not(:placeholder-shown){
    ....
}

If supporting legacy browsers is not needed, you could use a combination of required, valid, and invalid.

The good thing about using this is the valid and invalid pseudo-elements work well with the type attributes of input fields. For example:

input:invalid, textarea:invalid { 
    box-shadow: 0 0 5px #d45252;
    border-color: #b03535
}

input:valid, textarea:valid {
    box-shadow: 0 0 5px #5cd053;
    border-color: #28921f;
}

<input type="email" name="email" placeholder="[email protected]" required />
<input type="url" name="website" placeholder="http://johndoe.com"/>
<input type="text" name="name" placeholder="John Doe" required/>

For reference, JSFiddle here: http://jsfiddle.net/0sf6m46j/

This worked for me:

For the HTML, add the required attribute to the input element

<input class="my-input-element" type="text" placeholder="" required />

For the CSS, use the :invalid selector to target the empty input

input.my-input-element:invalid {

}

Notes:

• About required from w3Schools.com: "When present, it specifies that an input field must be filled out before submitting the form."

$('input#edit-keys-1').blur(function(){
    tmpval = $(this).val();
    if(tmpval == '') {
        $(this).addClass('empty');
        $(this).removeClass('not-empty');
    } else {
        $(this).addClass('not-empty');
        $(this).removeClass('empty');
    }
});

in jQuery. I added a class and styled with css.

.empty { background:none; }

It worked for me to add a class name to the input and then apply CSS rules to that:

<input type="text" name="product" class="product" />

<style>
input[value=""].product {
    display: none;
}
</style>

This question might have been asked some time ago, but as I recently landed on this topic looking for client-side form validation, and as the :placeholder-shown support is getting better, I thought the following might help others.

Using Berend idea of using this CSS4 pseudo-class, I was able to create a form validation only triggered after the user is finished filling it.

Here is ademo and explanation on CodePen: https://codepen.io/johanmouchet/pen/PKNxKQ

If you're happy not not supporting IE or pre-Chromium Edge (which might be fine if you are using this for progressive enhancement), you can use :placeholder-shown as Berend has said. Note that for Chrome and Safari you actually need a non-empty placeholder for this to work, though a space works.

*,
 ::after,
 ::before {
  box-sizing: border-box;
}

label.floating-label {
  display: block;
  position: relative;
  height: 2.2em;
  margin-bottom: 1em;
}

label.floating-label input {
  font-size: 1em;
  height: 2.2em;
  padding-top: 0.7em;
  line-height: 1.5;
  color: #495057;
  background-color: #fff;
  background-clip: padding-box;
  border: 1px solid #ced4da;
  border-radius: 0.25rem;
  transition: border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out;
}

label.floating-label input:focus {
  color: #495057;
  background-color: #fff;
  border-color: #80bdff;
  outline: 0;
  box-shadow: 0 0 0 0.2rem rgba(0, 123, 255, 0.25);
}

label.floating-label input+span {
  position: absolute;
  top: 0em;
  left: 0;
  display: block;
  width: 100%;
  font-size: 0.66em;
  line-height: 1.5;
  color: #495057;
  border: 1px solid transparent;
  border-radius: 0.25rem;
  transition: font-size 0.1s ease-in-out, top 0.1s ease-in-out;
}

label.floating-label input:placeholder-shown {
  padding-top: 0;
  font-size: 1em;
}

label.floating-label input:placeholder-shown+span {
  top: 0.3em;
  font-size: 1em;
}

<fieldset>
  <legend>
    Floating labels example (no-JS)
  </legend>
  <label class="floating-label">
    <input type="text" placeholder=" ">
    <span>Username</span>
  </label>
  <label class="floating-label">
    <input type="Password" placeholder=" ">
    <span>Password</span>
  </label>
</fieldset>
<p>
  Inspired by Bootstrap's <a href="https://getbootstrap.com/docs/4.0/examples/floating-labels/">floating labels</a>.
</p>

So I was playing around earlier with the new :where and :is clauses and conceived of this bit of fun, and after finding this post with the :invalid and :placeholder-shown bits, thought I might share this possibility for future reference

:required:where( input, textarea ):where( :placeholder-shown, :invalid ) {
    border-color: var(--warning);
}

which applies the :root { --warning: orange; } color to any required input or textarea, that is either empty or invalid. And that is just downright sexy

While no browser currently (2021-10-01) supports it, there is a proposal for a :blank pseudo-class.

ref: https://developer.mozilla.org/en-US/docs/Web/CSS/:blank. Do note, this is experimental, and no browser supports it as of now.

This is how you can make it possible. don't forget to set placeholder=" " and required attr to your inputs. you can change the props as you wish.

body{
    display: flex;
    justify-content: center;
    align-items: center;
}
.input-gp {
    margin-top: 150px;
    position: relative;
    
}
.input-gp input {
    position: relative;
    
}
.input-gp label{
    position: absolute;
    left: 5px;
    bottom: 5px;
    transition: all .4s ease;
}
.input-gp input:placeholder-shown + label{
    left: 10px;
    bottom: 5px;
}
.input-gp input:focus + label,
.input-gp input + label{
    bottom: 30px;
    left: 10px;
}

<body>
 <div class="input-gp ">
<input  type="email" name="" id="email" placeholder=" "       required>
   <label class=" position-absolute" for="email"> Email</label>
  </div>
  
 </body>

I'm wondered by answers we have clear attribute to get empty input boxes, take a look at this code

/*empty input*/
input:empty{
    border-color: red;
}
/*input with value*/
input:not(:empty){
    border-color: black;
}

UPDATE

input, select, textarea {
    border-color: @green;
    &:empty {
        border-color: @red;
    }
}

More over for having a great look in the validation

 input, select, textarea {
    &[aria-invalid="true"] {
        border-color: amber !important;
    }

    &[aria-invalid="false"], &.valid {
        border-color: green !important;
    }
}