:root {
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
               "Helvetica Neue", Arial, "Noto Sans", "PingFang SC",
               "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
}
body { font-family: var(--font-sans); }

/* optional stability tweaks */
.navbar-brand img { max-height: 48px; height: auto; }
img { max-width: 100%; height: auto; }