strapi/packages/strapi-admin/files/public/app/components/Header/styles.scss

// Import
@import "../../styles/variables/variables";

.header { /* stylelint-ignore */
  width: 100%;
  height: $header-height;
  position: fixed;
  z-index: 100;
  left: $left-menu-width;

  box-shadow:  0 1px 2px 0 rgba(40, 42, 49, 0.16);
  background-color: $white;

  line-height: $header-height;
}