First things first, open up your Glide app project. Head over to the screen where you want to tweak the CSS. Look for the screen options, then find the "Appearance" or "Settings" tab. There, you'll spot the “Custom CSS” section. That's your gateway to the CSS editor.

Now, in the CSS editor, you can start writing the CSS code you need to style your Glide app. For instance, if you want to change the background color of a button, you can add:

.button-classname {
    background-color: #FF5733;
}

To make sure your CSS hits the right elements, right-click on the elements in your browser and select "Inspect". This will show you the class names and IDs Glide uses. Use these in your CSS code.

If you want to apply styles across your whole app, write CSS rules for common elements like the body, headers, and paragraphs. For example:

body {
    font-family: 'Arial, sans-serif';
    background-color: #f0f0f0;
}

To keep your styling consistent, define CSS variables at the top of your CSS editor. This way, you can reuse values throughout your code easily:

:root {
    --primary-color: #0065ff;
    --secondary-color: #f0f0f0;
}

.button-classname {
    background-color: var(--primary-color);
}

Once you've written your CSS, save the changes in the editor. Then, preview your app to see how the custom styles look. Make any tweaks you need and save again.

Make sure your custom CSS looks good on different devices. Use media queries to adjust your styles for mobile and tablet views:

@media (max-width: 768px) {
    .button-classname {
        background-color: #FF5733;
        font-size: 14px;
    }
}

Test your app thoroughly to make sure the CSS doesn't mess up the layout or cause conflicts. Iterate on your CSS based on user feedback and further testing.