Edit in JSFiddle

function openRisiBank() {

  RisiBank.activate({

    // Use default options for Overlay + Dark
    // Other defaults are all combinations of Overlay/Modal/Frame and Light/Dark/LightClassic/DarkClassic, e.g. RisiBank.Defaults.Frame.LightClassic
    ...RisiBank.Defaults.Overlay.Dark,

    // Add selected image (risibank) to specified text area
    onSelectMedia: RisiBank.Actions.addRisiBankImageLink('#the-textarea'),
  });
}

<script src="https://risibank.fr/downloads/web-api/risibank.js"></script>

<div class="container">

    <!-- Button to trigger the overlay mode -->
    <a class="risibank-image"
       title="Ajouter un média RisiBank"
       onclick="openRisiBank(); return false;"
       href="javascript:void(0);"
    >
        <img src="https://risibank.fr/banner.png">
    </a>

    <!-- TextArea holding images -->
    <textarea id="the-textarea"></textarea>
</div>

.container {
    width: 600px;
    text-align: center;
}

.risibank-image img {
    width: 200px;
}

textarea {
    width: 100%;
    height: 80px;
}