odoo16/addons/website_event_track/views/event_track_templates_reminder.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

<!-- Options
    * reminder_light: no text displayed
    * reminder_small: text displayed as small
    * light_theme: bell is white/gold if set; otherwse bell is gray / white
 -->
<template id="track_widget_reminder">
    <t t-set="_btn_style" t-value="'btn-link' if reminder_light else (track.is_reminder_on and 'btn-primary') or 'btn-outline-primary'"/>
    <t t-set="_btn_size" t-value="'btn-sm' if reminder_small else ''"/>
    <div t-att-class="'o_wetrack_js_reminder btn %s %s' % (_btn_style, _btn_size)">
        <t t-if="track.is_reminder_on" t-set="title">Favorite On</t>
        <t t-else="track.is_reminder_on" t-set="title">Set Favorite</t>
        <i t-att-class="'fa fa-bell%s inactive_color_%s' % ('' if track.is_reminder_on else '-o', 'dark' if reminder_light and not light_theme else 'light')"
           t-att-data-track-id="track.id"
           t-att-title="title"
           t-att-data-is-reminder-light="reminder_light"
           t-att-data-reminder-on="bool(track.is_reminder_on)"></i>
        <span t-if="not reminder_light" class="o_wetrack_js_reminder_text">
            <t t-if="not track.is_reminder_on">
                Set Favorite
            </t><t t-else="">
                Favorite On
            </t>
        </span>
    </div>
</template>

</odoo>