@salesforce-ux/design-system/css/checkbox-button/base/touch.css

Salesforce Lightning Design System

/*! Lightning Design System 2.12.0 */
@charset "UTF-8";
.slds-checkbox-button {
  width: 2.75rem;
  height: 2.75rem;
}

.slds-checkbox_add-button {
  width: 2.75rem;
  height: 2.75rem;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-align: center;
  -ms-flex-align: center;
  align-items: center;
  -webkit-box-pack: center;
  -ms-flex-pack: center;
  justify-content: center;
}
.slds-checkbox_add-button .slds-checkbox_faux {
  width: 2rem;
  height: 2rem;
}