Thank you for reaching out.

To add a custom HTML and CSS to your website, please add the HTML and CSS to the Custom HTML block. Here is a screencast for your reference:
https://share.zight.com/qGubE2yL

You can add this HTML and CSS to the Custom HTML block and change the styling as preferred:

<button class="custom-button">Click Me</button>
<style>
.custom-button {
    background-color: #3498db;
    color: white;
    padding: 10px 20px;
    border: none;
    border-radius: 5px;
    font-size: 16px;
    cursor: pointer;
    transition: background-color 0.3s ease;
}

.custom-button:hover {
    background-color: #2980b9;
}
</style>

I hope this helps. Please let us know how we can help further.

Cheers,
Eze