Hi
1. You can use the following custom CSS, actually, now the background is already a solid color as same as the body background color.
.is-sticky .dgwork-product-tab{background:#Your Color;}
2. You can hide the item details tab by the following custom CSS
.dgwork-product-tab ul li:first-child{content:" ";}
.dgwork-product-tab ul li:nth-child(2){display:none;}
3. Just show the button by the following custom CSS
@media (max-width: 480px){
.is-sticky .dgwork-product-tab ul li.buy-button {
display: block;
}
}
You can put all custom CSS into style.css of your child theme or DGWork Options > Custom Code > Custom CSS.
Thanks