Additional CSS customization

I notice the Sydney theme comes with existing CSS under Customize > Additional CSS. Are these fixes to the original theme? Can I remove this CSS or is it needed due to upgrades? Below are examples of what edits are in this area:

    /* Header edits */
    #mainnav .current-menu-item {
    	border-bottom: 2px solid #D83A3A;

    #mainnav li {
    padding: 0 2px;
    margin: 0 12px;

    .site-header {
    border-bottom: 1px solid rgba(255,255,255,0.1);

    /* Skills edits */

    .skills_percentage_fix .elementor-progress-wrapper {
    	overflow: visible !important;

    .skills_percentage_fix .elementor-progress-percentage {
    	margin-top: -20px;
    	padding-right: 0;



Can you share a link to your website here, so I can check how that code works, and inspect whether that code can be removed safely or not?

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