Solution for this topic

To make the button edges round, use below CSS code instead of shared above.

#page-container .sh-nav li.menu-item-type-custom a {
 background-color: #000;
 padding: 0 10px;
 color: #fff;
 margin: 30px 0;
 border: 1px solid #DF343C;
 border-radius: 20px;
}

#page-container .sh-sticky-header-active:not(.sh-header-4):not(.sh-header-5):not(.sh-header-6) .sh-nav > li.menu-item-type-custom > a{
 margin: 15px 0;
}