html, body {
  height: 100%;
  margin: 0;
}

.site-wrapper {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* mainが伸びてfooterを押し下げる */
.site-main {
  flex: 1;
  display: block;
}

/* footerは下に置くだけ（固定しない） */
footer {
  width: 100%;
  text-align: center;
}

footer .nav-link {
  color: #00ff99;
  text-decoration: none;
  transition: color 0.3s;
}

footer .nav-link:hover {
  color: #00cc88;
}