move custom forms docs to the forms docs page

docs/components/forms.md

@@ -657,3 +657,137 @@ Block level help text for form controls.
 {% example html %}
 <p class="help-block">A block of help text that breaks onto a new line and may extend beyond one line.</p>
 {% endexample %}
+
+
+
+## Custom forms
+
+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.
+
+#### Checkboxes
+
+{% example html %}
+<label class="c-input c-checkbox">
+  <input type="checkbox">
+  <span class="c-indicator"></span>
+  Check this custom checkbox
+</label>
+{% endexample %}
+
+Custom checkboxes can also utilize the `:indeterminate` pseudo class.
+
+<div class="bd-example bd-example-indeterminate">
+  <label class="c-input c-checkbox">
+    <input type="checkbox">
+    <span class="c-indicator"></span>
+    Check this custom checkbox
+  </label>
+</div>
+
+**Heads up!** You'll need to set this state manually via JavaScript as there is no available HTML attribute for specifying it. If you're using jQuery, something like this should suffice:
+
+{% highlight js %}
+$('.your-checkbox').prop('indeterminate', true)
+{% endhighlight %}
+
+#### Radios
+
+{% example html %}
+<label class="c-input c-radio">
+  <input id="radio1" name="radio" type="radio">
+  <span class="c-indicator"></span>
+  Toggle this custom radio
+</label>
+<label class="c-input c-radio">
+  <input id="radio2" name="radio" type="radio">
+  <span class="c-indicator"></span>
+  Or toggle this other custom radio
+</label>
+{% endexample %}
+
+#### Stacked
+
+Custom checkboxes and radios are inline to start. Add a parent with class `.c-inputs-stacked` to ensure each form control is on separate lines.
+
+{% example html %}
+<div class="c-inputs-stacked">
+  <label class="c-input c-radio">
+    <input id="radioStacked1" name="radio-stacked" type="radio">
+    <span class="c-indicator"></span>
+    Toggle this custom radio
+  </label>
+  <label class="c-input c-radio">
+    <input id="radioStacked2" name="radio-stacked" type="radio">
+    <span class="c-indicator"></span>
+    Or toggle this other custom radio
+  </label>
+</div>
+{% endexample %}
+
+### Select menu
+
+Similar to the checkboxes and radios, we wrap the `<select>` in a `<label>` as a semantic wrapper that we can generate custom styles on with CSS's generated content.
+
+{% example html %}
+<label class="select">
+  <select>
+    <option selected>Open this select menu</option>
+    <option value="1">One</option>
+    <option value="2">Two</option>
+    <option value="3">Three</option>
+  </select>
+</label>
+{% endexample %}
+
+The `<select>` has quite a few styles to override and includes a few hacks to get things done. Here's what's happening:
+
+- The `appearance` is reset to `none` for nearly all styles to correctly apply across modern browsers (meaning not IE9).
+- The `:-moz-focusring` is overridden so that on focus there's no inner border in Firefox.
+- The arrow is hidden in Firefox with a media query hack. (There's a [longstanding open bug](https://bugzilla.mozilla.org/show_bug.cgi?id=649849) for a native method of addressing this.)
+- The arrow is hidden in IE10+ with a simple selector.
+- The arrow is hidden in IE9 with a separate media query hack which generates another pseudo-element to literally mask it. Not ideal, but doable.
+
+**Heads up!** This one comes with some quirks right now:
+
+- `select[multiple]` is currently currently **not supported**.
+- Clickability is limited in IE9.
+- Firefox's dropdown of `option`s looks rather ugly.
+- The custom caret is unable to receive the selected state's `color`.
+
+Any ideas on improving these are most welcome.
+
+### File browser
+
+{% example html %}
+<label class="file">
+  <input type="file" id="file">
+  <span class="file-custom"></span>
+</label>
+{% endexample %}
+
+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.
+