Trying to add some html and CSS to Custom Block

I have OJS 3.2.1.2, and I´m trying to upload this code to the Custom Block:

.flex-container {
display: flex;
background-color: #fff;
}

.flex-container > span {
margin: 4px;
text-align:center;
font-size: 50px;
color: #95a5a6;
}

a, a:hover, a:focus, a:active {
text-decoration: none;
color: inherit;
}

<span>
    <a href="https://www.facebook.com/RevistaAyrampu/" target="_blank"><i class="fab fa-facebook-square"></i></a>
</span>

<span>
    <a href="https://www.instagram.com/revistaayrampu/" target="_blank"><i class="fab fa-instagram-square"></i></a>
</span>

<span>
    <a href="https://mail.google.com/mail/u/0/?view=cm&fs=1&tf=1&source=mailto&to=equipoeditorial@ayrampu.org" target="_blank"><i class="fas fa-envelope-square"></i></a>
</span>

But it does not work, when a reopen the code custom block window the code is incomplete.
Is there some restriction?
I will appreciate your help

Rennzo Rojas
Kaypunku Lab

Hi @rennzorojas,

You may wish to see the suggestions in this post here:

It might be more better to use the existing CSS structure for the custom block.

Best regards,

Roger