nextcloud/apps/calendar/templates/part.editevent.php

<div id="event" title="<?php echo $l->t("Edit an event");?>">
	<form id="event_form">
		<input type="hidden" name="id" value="<?php echo $_['id'] ?>">
<?php echo $this->inc("part.eventform"); ?>
	<div style="width: 100%;text-align: center;color: #FF1D1D;" id="errorbox"></div>
	<span id="actions">
		<input type="button" class="submit" style="float: left;" value="<?php echo $l->t("Submit");?>" onclick="validate_event_form('ajax/editevent.php');">
	</span>
	</form>
</div>