Change Bootstrap input focus blue glow

Question

In the end I changed the following css entry in bootstrap.css

textarea:focus,
input[type="text"]:focus,
input[type="password"]:focus,
input[type="datetime"]:focus,
input[type="datetime-local"]:focus,
input[type="date"]:focus,
input[type="month"]:focus,
input[type="time"]:focus,
input[type="week"]:focus,
input[type="number"]:focus,
input[type="email"]:focus,
input[type="url"]:focus,
input[type="search"]:focus,
input[type="tel"]:focus,
input[type="color"]:focus,
.uneditable-input:focus {   
  border-color: rgba(126, 239, 104, 0.8);
  box-shadow: 0 1px 1px rgba(0, 0, 0, 0.075) inset, 0 0 8px rgba(126, 239, 104, 0.6);
  outline: 0 none;
}

You can use the .form-control selector to match all inputs. For example to change to red:

.form-control:focus {
  border-color: #FF0000;
  box-shadow: inset 0 1px 1px rgba(0, 0, 0, 0.075), 0 0 8px rgba(255, 0, 0, 0.6);
}

Put it in your custom css file and load it after bootstrap.css. It will apply to all inputs including textarea, select etc...

If you are using Bootstrap 3.x, you can now change the color with the new @input-border-focus variable.

See the commit for more info and warnings.

In _variables.scss update @input-border-focus.

To modify the size/other parts of this glow modify the mixins/_forms.scss

@mixin form-control-focus($color: $input-border-focus) {
  $color-rgba: rgba(red($color), green($color), blue($color), .6);
  &:focus {
    border-color: $color;
    outline: 0;
    @include box-shadow(inset 0 1px 1px rgba(0,0,0,.075), 0 0 4px $color-rgba);
  }
}

You can modify the .form-control:focus color without altering the bootstrap style in this way:

Quick fix

.form-control:focus {
        border-color: #28a745;
        box-shadow: 0 0 0 0.2rem rgba(40, 167, 69, 0.25);
    } 

Full explanation

1. Find the bootstrapCDN version that you are using. E.g. for me right now is 4.3.1: https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.css
2. Search for the class you want to modify. E.g. .form-control:focus and copy the parameters that you want to modify into your css. In this case is border-color and box-shadow.
3. Choose a color for the border-color. In this case I choose to pick up the same green the bootstrap uses for their .btn-success class, by searching for that particular class in the bootstrap.css page mentioned in the step 1.
4. Convert the color you have picked to RGB and add that to the box-shadow parameter without altering the fourth RGBA parameter (0.25) that bootstrap has for transparency.

For Bootstrap v4.0.0 beta release you will need the following added to a stylesheet that overrides Bootstrap (either add in after CDN/local link to bootstrap v4.0.0 beta or add !important to the stylings:

.form-control:focus {
  border-color: #6265e4 !important;
  box-shadow: 0 0 5px rgba(98, 101, 228, 1) !important;
}

Replace the border-color and the rgba on the box-shadow with which ever colour style you'd like*.