Per @weaverryan's call to action on twitter and slack discussion.

It's been tricky to create a generic form layout for tailwind as it's a css utility framework and has an unlimited number of ways to style forms. With tailwindcss 2.0, the tailwind team released an official form plugin that provides form element reset/normalization that looks decent out of the box. This PR is an attempt to piggy-back on this plugin to provide a minimal Symfony form layout for tailwind. The goal is to have your forms look good in a tailwind/Symfony app with no customization (but of course allow customization as desired).

This layout requires tailwindcss 2 and the form plugin.

I followed the "unstyled" demo for the form plugin as a style guide. Here is a screenshot of this layout used in a demo Symfony app with several common form types (I'll try to keep this updated as I update the PR):

Some notes about the layout:

1. I tried to use as few tailwind classes as possible and avoid color (primary exception being the error color).
2. I decided on a mobile-first approach so out of the box, it will look decent on any device and drastically reduces the number of css classes/assumptions.
3. While other layouts merge classes passed by the user, I opted to replace. This ensures the user doesn't have to undo the class decisions made by this layout. I also discovered "undoing" doesn't work as I expected anyway: class="mt-1 mt-0", mt-1 "wins" as mt-1 comes later in the compiled stylesheet.
4. For the low level blocks, I extracted the classes into their own "variables" (row_class, widget_class, label_class, help_class, error_item_class) to make it easier to extend and customize the layout. Note the widget_disabled_class/widget_errors_class variables: these are added even if you've overridden the widget_class variable.

Customization

Customizing is especially important for this layout. Here are the two ways:

1. Twig form functions:

   {{ form_row(form.title, {
       row_class: 'my row classes',
       label_class: 'my label classes',
       error_item_class: 'my error item classes',
       widget_class: 'my widget classes',
       widget_disabled_class: 'my disabled widget classes',
       widget_errors_class: 'my widget with error classes',
   }) }}
2. Project specific form layout:

   {% use 'tailwind_2_layout.html.twig' %}
   
   {%- block form_row -%}
       {%- set row_class = row_class|default('my row classes') -%}
       {{- parent() -}}
   {%- endblock form_row -%}
   
   {%- block widget_attributes -%}
       {%- set widget_class = widget_class|default('my widget classes') -%}
       {%- set widget_disabled_class = widget_disabled_class|default('my disabled widget classes') -%}
       {%- set widget_errors_class = widget_errors_class|default('my widget with error classes') -%}
       {{- parent() -}}
   {%- endblock widget_attributes -%}
   
   {%- block form_label -%}
       {%- set label_class = label_class|default('my label classes') -%}
       {{- parent() -}}
   {%- endblock form_label -%}
   
   {%- block form_help -%}
       {%- set help_class = help_class|default('my label classes') -%}
       {{- parent() -}}
   {%- endblock form_help -%}
   
   {%- block form_errors -%}
       {%- set error_item_class = error_item_class|default('my error item classes') -%}
       {{- parent() -}}
   {%- endblock form_errors -%}

Customization POC/Demo

With this custom form theme:

{%- block form_label -%}
    {%- set label_class = label_class|default('block text-gray-500 uppercase tracking-wider text-sm font-bold') -%}
    {{- parent() -}}
{%- endblock -%}

{%- block widget_attributes -%}
    {%- set widget_class = widget_class|default('mt-1 block w-full rounded-md border-gray-300 shadow-sm focus:border-indigo-300 focus:ring focus:ring-indigo-200 focus:ring-opacity-50') -%}
    {{- parent() -}}
{%- endblock -%}

{%- block checkbox_widget -%}
    {%- set widget_class = widget_class|default('mr-2 rounded border-gray-300 text-indigo-600 shadow-sm focus:border-indigo-300 focus:ring focus:ring-offset-0 focus:ring-indigo-200 focus:ring-opacity-50') -%}
    {{- parent() -}}
{%- endblock -%}

{%- block checkbox_label -%}
    {%- set label_class = label_class|default('block text-gray-800') -%}
    {{- block('form_label') -}}
{%- endblock -%}

The above example looks like this: