Change cart icon by custom-theme’s _extend.less

I have built a custom-theme that extended from luma. However, I can’t change cart icon by _extends.less of the custom-theme. May I know is somewhere else to change cart icon?

app/design/frontend///web/css/source/_extends.less:

.minicart-wrapper {
margin-right: 10px;

.action.showcart::before, .action.showcart.active::before {
    display: inline-block;
    white-space: nowrap;
    word-wrap: normal;
    direction: ltr;
    content: 'e613';
    color: @color-white;
    -moz-font-feature-settings: 'liga';
    -moz-osx-font-smoothing: grayscale;
    vertical-align: middle;
}}