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(For quantity), Replace span counter number tag with
<span class="counter-number">
<!-- ko if: getCartParam('summary_count') < 100 -->
<!-- ko text: getCartParam('summary_count') --><!-- /ko -->
<!-- /ko -->
<!-- ko if: getCartParam('summary_count') > 99 -->
<!-- ko text: '99+' --><!-- /ko -->
<!-- /ko -->
</span>
& for items, replace counter label tag with below code.
<span class="counter-label">
<!-- ko if: getCartParam('summary_count') == 1 -->
<!-- ko i18n: 'item' --><!-- /ko -->
<!-- /ko -->
<!-- ko if: getCartParam('summary_count') > 1 -->
<!-- ko i18n: 'items' --><!-- /ko -->
<!-- /ko -->
</span>