The Kinetic Lightswitch

Module 3 of 6 in the KINETIC.email developer course. Learn how to detect whether an email client supports kinetic interactivity and provide appropriate fallbacks.

What is the Kinetic Lightswitch?

The Kinetic Lightswitch is a mechanism that detects whether an email client supports interactive elements, then shows either the interactive content or a fallback version. Not every client supports the CSS selectors kinetic email needs, so the lightswitch uses a hidden checkbox as a state-detection system that decides automatically, when the email opens, which version to display.

If kinetic works

• The interactive version is displayed.
• The fallback version is hidden.
• Users get the full interactive experience.

If kinetic does not work

• The interactive version stays hidden.
• The fallback version is displayed.
• Users still get a functional experience.

Implementing the lightswitch

HTML structure

<input type="checkbox" class="kinetic"
       name="interactive" id="Kinetic" checked>

<table role="presentation" width="100%">
  <tr class="interactive"><td>Kinetic content</td></tr>
  <tr class="fallback"><td>Fallback content</td></tr>
</table>

CSS rules

.fallback { display: table-row !important; }
.interactive {
  display: none !important;
  max-height: 0 !important;
  overflow: hidden !important;
}
#Kinetic:checked ~ * .interactive {
  display: table-row !important;
  max-height: none !important;
  overflow: visible !important;
}
#Kinetic:checked ~ * .fallback {
  display: none !important;
}

The logic

1. The hidden checkbox: a checkbox that is checked by default and hidden from view.
2. Conditional display: CSS shows the interactive content only if the checkbox is checked and the client supports :checked and the general sibling selector.
3. Automatic detection: clients that do not support those selectors ignore the rules, so the fallback stays visible.

The approach is automatic. No user interaction is needed: a client that cannot do kinetic email simply ignores the selectors it does not understand. The lesson's live demo exposes a "Toggle Lightswitch" button so you can simulate an unsupported client; unchecked means the fallback is shown. In a real email there is no toggle. For the demo's own content swap, the lesson uses the accessible hiding pattern (max-height: 0; opacity: 0; overflow: hidden) instead of display: none so content stays available to screen readers.

Hands-on exercises

Exercise 1: Build the lightswitch

Add a checkbox with class="kinetic", id="Kinetic" and the checked attribute. Then write a #Kinetic:checked ~ .interactive rule that reveals the interactive block (max-height: none, opacity: 1, overflow: visible) and a #Kinetic:checked ~ .fallback rule that hides the fallback (max-height: 0, opacity: 0, overflow: hidden).

Exercise 2: Add a preview toggle

Add a <label for="Kinetic"> reading "Toggle Preview" so you can test both versions, add transition: all 0.4s ease to both blocks for smooth switching, and color the label #10b981 while the interactive version is active.

Best practices

Implementation tips

• Always include a fallback for non-supporting clients.
• Place the lightswitch at the top of your HTML so detection works properly.
• Use !important on display properties to override client-specific styles.
• Match the display value to the element: show a <tr> with display: table-row, a <div> or <td> with display: block; hiding is always display: none. KineticAI puts the interactive and fallback pair on table rows, so production emails use table-row. Using block on a row pops it out of the table layout and renders it at content width instead of full width.
• Test in multiple clients to verify the lightswitch works.

Common pitfalls

• Forgetting the fallback.
• Using overly complex selectors that behave inconsistently across clients.
• Not testing in the major email clients.
• Overcomplicating the fallback so it is hard to maintain.

Pro tip: use separate tracking pixels or links in each version to learn how many subscribers see the kinetic version versus the fallback.

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