size of the button

Hi

Please take a look at this post in your desktop:
https://trekpyrenees.unimbohosting.net/fr/haute-bergueda/

If you go at the bottom of the post you will see the button “JE VEUX EN SAVOUR PLUS” is out of the side bar on the right.

The button has been createt with this code:

<div style=”width:100%; text-align:center”>
<p>[submit “Je veux en savoir plus”]</p>
</div>

If I watch the post in an smartphone, it looks OK because the side bar is not used.

What can I do to see the button OK when in desktop?

Thanks