Bootstrap's form controls expand on [our Rebooted form styles]({{ site.baseurl }}/content/reboot/#forms) with classes. Use these classes to opt into their customized displays for a more consistent rendering across browsers and devices. The example form below demonstrates common HTML form elements that receive updated styles from Bootstrap with additional classes.
<smallclass="text-muted">This is some placeholder block-level help text for the above input. It's a bit lighter and easily wraps to a new line.</small>
Below is a complete list of the specific from controls supported by Bootstrap and the classes that customize them. Additional documentation is available for each group.
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<th>Classes</th>
<th>Used for</th>
<th>Supported variations</th>
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{% markdown %}`.form-group`{% endmarkdown %}
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Any group of form controls
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{% markdown %}Use with any block-level element like `<fieldset>` or `<div>`{% endmarkdown %}
Since Bootstrap applies `display: block` and `width: 100%` to almost all our form controls, forms will by default stack vertically. Additional classes can be used to vary this layout on a per-form basis.
### Form groups
The `.form-group` class is the easiest way to add some structure to forms. It's only purpose is to provide `margin-bottom` around a label and control pairing. As a bonus, since it's a class you can use it with `<fieldset>`s, `<div>`s, or nearly any other element.
Use the `.inline-form` class to to display a series of labels, form controls, and buttons on a single horizontal row. Form controls within inline forms behave differently:
- Controls are `display: inline-block` to provide alignment control via `vertical-align` and `margin`.
- Controls receive `width: auto` to override the Bootstrap default `width: 100%`.
- Controls **only appear inline in viewports that are at least 768px wide** to account for narrow viewports on mobile devices.
Because of this, you may need to manually address the width and alignment of individual form controls. Lastly, as shown below, you should always include a `<label>` with each form control.
For more structured form layouts, you can utilize Bootstrap's predefined grid classes (or mixins). Add the `.row` class to form groups and use the `.col-*` classes to specify the width of your labels and controls. To vertically center the labels with the textual inputs—nearly anything with `.form-control`—use the `.form-control-label` class.
Disabled checkboxes and radios are supported, but to provide a "not-allowed" cursor on hover of the parent `<label>`, you'll need to add the <code>.disabled</code> class to the parent `.radio`, `.radio-inline`, `.checkbox`, or `.checkbox-inline`.
By default, browsers will treat all native form controls (`<input>`, `<select>` and `<button>` elements) inside a `<fieldset disabled>` as disabled, preventing both keyboard and mouse interactions on them. However, if your form also includes `<a ... class="btn btn-*">` elements, these will only be given a style of `pointer-events: none`. As noted in the section about [disabled state for buttons](../buttons/#disabled-state) (and specifically in the sub-section for anchor elements), this CSS property is not yet standardized and isn't fully supported in Opera 18 and below, or in Internet Explorer 11, and won't prevent keyboard users from being able to focus or activate these links. So to be safe, use custom JavaScript to disable such links.
While Bootstrap will apply these styles in all browsers, Internet Explorer 11 and below don't fully support the `disabled` attribute on a `<fieldset>`. Use custom JavaScript to disable the fieldset in these browsers.
Add the `readonly` boolean attribute on an input to prevent modification of the input's value. Read-only inputs appear lighter (just like disabled inputs), but retain the standard cursor.<
No official help text classes exist in Bootstrap 4 (previously we had `.help-block` in v3), but thanks to our utility classes like `.text-muted`, you can create much more flexible help text as you need it.
Inline text can use any typical inline HTML element (be it a `<small>`, `<span>`, or something else).
Bootstrap includes validation styles for error, warning, and success states on form controls. To use, add `.has-warning`, `.has-error`, or `.has-success` to the parent element. Any `.control-label`, `.form-control`, and `.text-help` within that element will receive the validation styles.
#### Conveying validation state to assistive technologies and colorblind users
Using these validation styles to denote the state of a form control only provides a visual, color-based indication, which will not be conveyed to users of assistive technologies - such as screen readers - or to colorblind users.
Ensure that an alternative indication of state is also provided. For instance, you can include a hint about state in the form control's `<label>` text itself (as is the case in the following code example), include a [Glyphicon](../components/#glyphicons) (with appropriate alternative text using the `.sr-only` class - see the [Glyphicon examples](../components/#glyphicons-examples)), or by providing an additional [help text](#forms-help-text) block. Specifically for assistive technologies, invalid form controls can also be assigned an `aria-invalid="true"` attribute.
For even more customization and cross browser consistency, use our completely custom form elements to replace the browser defaults. They're built on top of semantic and accessible markup, so they're solid replacements any default form control.
### Checkboxes and radios
Each checkbox and radio is wrapped in a `<label>` for three reasons:
- It provides a larger hit areas for checking the control.
- It provides a helpful and semantic wrapper to help us replace the default `<input>`s.
- It triggers the state of the `<input>` automatically, meaning no JavaScript is required.
We hide the default `<input>` with `opacity` and use the `.c-indicator` to build a new custom form control. We can't build a custom one from just the `<input>` because CSS's `content` doesn't work on that element.
With the sibling selector (`~`), we use the `:checked` state to trigger a makeshift checked state on the custom control.
In the checked states, we use **base64 embedded SVG icons** from [Open Iconic](http://useiconic.com/open). This provides us the best control for styling and positioning across browsers and devices.
Custom checkboxes can also utilize the `:indeterminate` pseudo class when manually set via JavaScript (there is no available HTML attribute for specifying it).
Custom selects degrade nicely in IE9, receiving only a handful of overrides to remove the custom `background-image`. **Multiple selects (e.g., `<select multiple>`) are not currently supported.**
The file input is the most gnarly of the bunch. Here's how it works:
- We wrap the `<input>` in a `<label>` so the custom control properly triggers the file browser.
- We hide the default file `<input>` via `opacity`.
- We use `:after` to generate a custom background and directive (*Choose file...*).
- We use `:before` to generate and position the *Browse* button.
- We declare a `height` on the `<input>` for proper spacing for surrounding content.
In other words, it's an entirely custom element, all generated via CSS.
**Heads up!** The custom file input is currently unable to update the *Choose file...* text with the filename. Without JavaScript, this might not be possible to change, but I'm open to ideas.
