Adding asterisk to required fields in Bootstrap 3

Question

Use .form-group.required without the space.

.form-group.required .control-label:after {
  content:"*";
  color:red;
}

Edit:

For the checkbox you can use the pseudo class :not(). You add the required * after each label unless it is a checkbox

.form-group.required:not(.checkbox) .control-label:after, 
.form-group.required .text:after { /* change .text in whatever class of the text after the checkbox has */
   content:"*";
   color:red;
}

Note: not tested

You should use the .text class or target it otherwise probably, try this html:

<div class="form-group required">
   <label class="col-md-2 control-label">&#160;</label>
   <div class="col-md-4">
      <div class="checkbox">
         <label class='text'> <!-- use this class -->
            <input class="" id="id_tos" name="tos" required="required" type="checkbox" /> I have read and agree to the Terms of Service
         </label>
      </div>
   </div>
</div>

Ok third edit:

CSS back to what is was

.form-group.required .control-label:after { 
   content:"*";
   color:red;
}

HTML:

<div class="form-group required">
   <label class="col-md-2">&#160;</label> <!-- remove class control-label -->
   <div class="col-md-4">
      <div class="checkbox">
         <label class='control-label'> <!-- use this class as the red * will be after control-label -->
            <input class="" id="id_tos" name="tos" required="required" type="checkbox" /> I have read and agree to the Terms of Service
         </label>
      </div>
   </div>
</div>

Assuming this is what the HTML looks like

<div class="form-group required">
   <label class="col-md-2 control-label">E-mail</label>
   <div class="col-md-4"><input class="form-control" id="id_email" name="email" placeholder="E-mail" required="required" title="" type="email" /></div>
</div>

To display an asterisk on the right of the label:

.form-group.required .control-label:after { 
    color: #d00;
    content: "*";
    position: absolute;
    margin-left: 8px;
    top:7px;
}

Or to the left of the label:

.form-group.required .control-label:before{
   color: red;
   content: "*";
   position: absolute;
   margin-left: -15px;
}

To make a nice big red asterisks you can add these lines:

font-family: 'Glyphicons Halflings';
font-weight: normal;
font-size: 14px;

Or if you are using Font Awesome add these lines (and change the content line):

font-family: 'FontAwesome';
font-weight: normal;
font-size: 14px;
content: "\f069";

.form-group .required .control-label:after should probably be .form-group.required .control-label:after. The removal of the space between .form-group and .required is the change.

The other two answers are correct. When you include spaces in your CSS selectors you're targeting child elements so:

.form-group .required {
    styles
}

Is targeting an element with the class of "required" that is inside an element with the class of "form-group".

Without the space it's targeting an element that has both classes. 'required' and 'form-group'

use simple css,

.myform .required:after {
  content: " *";
    color: red;
    font-weight: 100;
}

 <form class="myform">
    <div class="col-md-12">
      <label for="xxx_fname" class="form-label required">First Name</label>
      <input type="text" class="form-control" id="xxx_fname" >
   </div>
    <div class="col-md-12">
      <label for="xxx_lname" class="form-label required">Last Name</label>
      <input type="text" class="form-control" id="xxx_lname" >
   </div>
</form

This CSS worked for me:

.form-group.required.control-label:before{
   color: red;
   content: "*";
   position: absolute;
   margin-left: -10px;
}

and this HTML:

<div class="form-group required control-label">
  <label for="emailField">Email</label>
  <input type="email" class="form-control" id="emailField" placeholder="Type Your Email Address Here" />
</div>