Align and center ‘add to cart’ button

I want to alight and center the ‘add to cart’ button.
Now the button is on the left side of the products instead of centered in the middle.
Also 1 button is higher/lower then the other one.
First priority is to center the button in the middle.
To give a exaple, this is how it looks now: https://www.model-kits.nl
The buttons are on the left side instead of centered.
I have the Astra theme.
No CSS is working.
I tried:

.single.woocommerce div.product form.cart .button {
margin: auto;
flex: 1; /* remove this if you do not want to fill the space */
}

and

#top.single-product form.cart {
    display: flex;
    float: none;
    align-items: center;
    justify-content: center;
}

#top.single-product form.cart .quantity, 
#top.single-product form.cart .quantity * {
    margin-bottom: 0;
}

and

.woocommerce ul.products li.product {
display: block;
}

Anyone can help me with it?
I don’t use plugin that conflict with buttons or something.
Hope someone can help me.