Resizing button for mobile

Site URL: https://callahan-soft-opening.squarespace.com/private

Hey there, 

I'm hoping someone can help me with something minor that's stumping me.

I have a button to our company's sister co. that is way too big in mobile. I've tried a number of different codes that haven't worked, starting with variations of other media queries I have used to modify our mobile site. 

Attached two screenshots where you can see how the size of the mobile view button is large enough to result in a sideways scroll, which is particularly annoying. 

I've been working on iterations for this site for our company for a long time and worried there's something buried in the css that is screwing this up.

Thanks ahead for anyone who will put a second set of eyes to this for me. 

pw: password

Hi,Add to Design > Custom CSS

/* resize take me to on mobile */
@media screen and (max-width:640px) {
div#block-yui_3_17_2_1_1630000245380_10838 {
    width: 50%;
    margin: 0 auto;
}
}