Hello There,
We have tested this code before we gave it to you.
#Video-Container .Featured-Videos .Video-Button {
margin: 0;
position: absolute;
top: 50%;
left: 50%;
margin-left: -25%;
margin-top: -25%;
}
The result of this in looks like this one smaller screen

If in your test it doesn’t work, please try to test it using Chrome’s incognito mode in your mobile phone.
If it is still doesn’t work out, please replace that code and add the following css code in the customizer, Appearance > Customize > Custom > CSS
#Video-Container .Featured-Videos .Video-Button {
margin: 0;
position: absolute;
top: 50%;
left: 50%;
width: 112px;
height: 112px;
margin-left: -56px;
margin-top: -56px;
}
Please let us know how it goes.