Without a link to your site it’s hard to offer advice.
Rather than attempting to alter the position of the item on each size. A simple solution in these cases is often to put the button in both places, and use CSS media queries to hide and show them at the screen sizes you need.
Something like:
/*Hide mobile button on desktop*/
#mobile-button {
display: none;
}
/*Hide the desktop button and show the mobile button on mobile*/
@media (max-width: 740px) {
#desktop-button {
display: none;
}
#mobile-button {
display: block;
}
}
Thanks a lot for your answer! mishkajewelry.com - here is my shop. when opened on mobile “shop now” button appears below the header and with no border and if I change the text color to white then it’s not visible at all. So what want is to have this button with black text and black borders on mobile, but with white borders and white text on desktop.