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Customizing your demo with CSS and Javascript

Gradio allows you to customize your demo in several ways. You can customize the layout of your demo, add custom HTML, and add custom theming as well. This tutorial will go beyond that and walk you through how to add custom CSS and JavaScript code to your demo in order to add custom styling, animations, custom UI functionality, analytics, and more.

Adding custom CSS to your demo

Gradio themes are the easiest way to customize the look and feel of your app. You can choose from a variety of themes, or create your own. To do so, pass the theme= kwarg to the Blocks constructor. For example:

with gr.Blocks(theme=gr.themes.Glass()):

Gradio comes with a set of prebuilt themes which you can load from gr.themes.*. You can extend these themes or create your own themes from scratch - see the Theming guide for more details.

For additional styling ability, you can pass any CSS to your app using the css= kwarg. You can either the filepath to a CSS file, or a string of CSS code.

Warning: The use of query selectors in custom JS and CSS is not guaranteed to work across Gradio versions as the Gradio HTML DOM may change. We recommend using query selectors sparingly.

The base class for the Gradio app is gradio-container, so here’s an example that changes the background color of the Gradio app:

with gr.Blocks(css=".gradio-container {background-color: red}") as demo:

If you’d like to reference external files in your css, preface the file path (which can be a relative or absolute path) with "file=", for example:

with gr.Blocks(css=".gradio-container {background: url('file=clouds.jpg')}") as demo:

Note: By default, files in the host machine are not accessible to users running the Gradio app. As a result, you should make sure that any referenced files (such as clouds.jpg here) are either URLs or allowed via the allow_list parameter in launch(). Read more in our section on Security and File Access.

The elem_id and elem_classes Arguments

You can elem_id to add an HTML element id to any component, and elem_classes to add a class or list of classes. This will allow you to select elements more easily with CSS. This approach is also more likely to be stable across Gradio versions as built-in class names or ids may change (however, as mentioned in the warning above, we cannot guarantee complete compatibility between Gradio versions if you use custom CSS as the DOM elements may themselves change).

css = """
#warning {background-color: #FFCCCB}
.feedback textarea {font-size: 24px !important}

with gr.Blocks(css=css) as demo:
    box1 = gr.Textbox(value="Good Job", elem_classes="feedback")
    box2 = gr.Textbox(value="Failure", elem_id="warning", elem_classes="feedback")

The CSS #warning ruleset will only target the second Textbox, while the .feedback ruleset will target both. Note that when targeting classes, you might need to put the !important selector to override the default Gradio styles.

Adding custom JavaScript to your demo

There are 3 ways to add javascript code to your Gradio demo:

  1. You can add JavaScript code as a string or as a filepath to the js parameter of the Blocks or Interface initializer. This will run the JavaScript code when the demo is first loaded.

Below is an example of adding custom js to show an animated welcome message when the demo first loads.

import gradio as gr

def welcome(name):
    return f"Welcome to Gradio, {name}!"

js = """
function createGradioAnimation() {
    var container = document.createElement('div'); = 'gradio-animation'; = '2em'; = 'bold'; = 'center'; = '20px';

    var text = 'Welcome to Gradio!';
    for (var i = 0; i < text.length; i++) {
                var letter = document.createElement('span');
       = '0';
       = 'opacity 0.5s';
                letter.innerText = text[i];


                setTimeout(function() {
           = '1';
                }, 50);
            }, i * 250);

    var gradioContainer = document.querySelector('.gradio-container');
    gradioContainer.insertBefore(container, gradioContainer.firstChild);

    return 'Animation created';
with gr.Blocks(js=js) as demo:
    inp = gr.Textbox(placeholder="What is your name?")
    out = gr.Textbox()
    inp.change(welcome, inp, out)


Note: You can also supply your custom js code as a file path. For example, if you have a file called custom.js in the same directory as your Python script, you can add it to your demo like so: with gr.Blocks(js="custom.js") as demo:. Same goes for Interface (ex: gr.Interface(..., js="custom.js")).

  1. When using Blocks and event listeners, events have a js argument that can take a JavaScript function as a string and treat it just like a Python event listener function. You can pass both a JavaScript function and a Python function (in which case the JavaScript function is run first) or only Javascript (and set the Python fn to None). Take a look at the code below:
import gradio as gr

blocks = gr.Blocks()

with blocks as demo:
    subject = gr.Textbox(placeholder="subject")
    verb = gr.Radio(["ate", "loved", "hated"])
    object = gr.Textbox(placeholder="object")

    with gr.Row():
        btn = gr.Button("Create sentence.")
        reverse_btn = gr.Button("Reverse sentence.")
        foo_bar_btn = gr.Button("Append foo")
        reverse_then_to_the_server_btn = gr.Button(
            "Reverse sentence and send to server."

    def sentence_maker(w1, w2, w3):
        return f"{w1} {w2} {w3}"

    output1 = gr.Textbox(label="output 1")
    output2 = gr.Textbox(label="verb")
    output3 = gr.Textbox(label="verb reversed")
    output4 = gr.Textbox(label="front end process and then send to backend"), [subject, verb, object], output1)
        None, [subject, verb, object], output2, js="(s, v, o) => o + ' ' + v + ' ' + s"
    verb.change(lambda x: x, verb, output3, js="(x) => [...x].reverse().join('')"), [], subject, js="(x) => x + ' foo'")
        [subject, verb, object],
        js="(s, v, o) => [s, v, o].map(x => [...x].reverse().join(''))",


  1. Lastly, you can add JavaScript code to the head param of the Blocks initializer. This will add the code to the head of the HTML document. For example, you can add Google Analytics to your demo like so:
head = f"""
<script async src="{google_analytics_tracking_id}"></script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){{dataLayer.push(arguments);}}
  gtag('js', new Date());
  gtag('config', '{google_analytics_tracking_id}');

with gr.Blocks(head=head) as demo:
    ...demo code...

The head parameter accepts any HTML tags you would normally insert into the <head> of a page. For example, you can also include <meta> tags to head.

Note that injecting custom HTML can affect browser behavior and compatibility (e.g. keyboard shortcuts). You should test your interface across different browsers and be mindful of how scripts may interact with browser defaults. Here’s an example where pressing Shift + s triggers the click event of a specific Button component if the browser focus is not on an input component (e.g. Textbox component):

import gradio as gr

shortcut_js = """
function shortcuts(e) {
    var event = document.all ? window.event : e;
    switch ( {
        case "input":
        case "textarea":
        if (e.key.toLowerCase() == "s" && e.shiftKey) {
document.addEventListener('keypress', shortcuts, false);

with gr.Blocks(head=shortcut_js) as demo:
    action_button = gr.Button(value="Name", elem_id="my_btn")
    textbox = gr.Textbox() : "button pressed", None, textbox)