<button name="action_offer_accept"

type="object"

icon="fa-check"

class="btn-success"

string="Accept"

invisible="can_accept == False or state == 'accepted'"

/>

<button name="action_offer_refuse"

type="object"

icon="fa-times"

class="btn-danger"

string="Refuse"

invisible="can_accept == False"

/>

<field name="can_accept" invisible="True"/>

If one of the buttons "action_offer_accept" and "action_offer_refuse" is initially invisible=True and the other is visible, the first one doesn't take any space and no space is reserved for it. After setting invisible=False, it appears in a "second line" in the layout which is visually very unappealing and inconsistent compared to the option that both buttons are initially visible and in one "line". 

How to always "reserve" space for my buttons action_offer_accept and action_offer_refuse?