Hi Stefano
There is no send button in HTML code. Does not look like CSS isuue.
<div class="tnp-submit">
<a href="?page=newsletter_emails_index" class="button"><i class="fa fa-chevron-left"></i> Back</a> <input class="button-primary" type="button" value="Save" onclick="this.form.act.value='save';this.form.submit()"> <input class="button-secondary" type="button" value="Save and test" onclick="this.form.btn.value='';this.form.act.value='test';if (confirm('Save and send test emails to test addresses?')) this.form.submit()">
<input class="button-secondary" type="button" value="Save and switch to HTML source editor" onclick="this.form.btn.value='';this.form.act.value='editor';if (confirm('Sure?')) this.form.submit()"> </div>