web/web_drop_target/static/src/xml/widgets.xml

<?xml version="1.0" encoding="UTF-8" ?>
<template>
    <t t-name="web_drop_target.drop_overlay">
        <div class="o_drag_over d-none">
            <div class="o_drag_over_content">
                <div>
                    <i class="fa fa-file-o fa-5x" aria-hidden="true" />
                </div>
                <div>
                    <t t-if="id">
                        <h2>Drop your files here</h2>
                    </t>
                    <t t-else="">
                        <h2>Please save the record before dropping a file</h2>
                    </t>
                </div>
            </div>
        </div>
    </t>
</template>