Add white border for mobilemenu and wishlist icon

.button.icon.circle>i:only-child {
    margin: 0;
    border: 1px solid white;
    padding: 3px;
}

To add or override CSS: use the “Additional CSS” option in the customizer.? https://codex.www.ads-software.com/CSS#Custom_CSS_in_WordPress

Learn to use the Chrome Developer Tools or Firefox Developer Tools to help you see and test changes to your CSS.