.login-box {
  position: fixed; /* changed from absolute to fixed so it centers relative to the viewport */
  align-items: center;
  justify-content: center;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%); /* center exactly */
  display: flex;
  width: 100%;
  max-width: 420px; /* keeps box from stretching too wide */
  padding: 1rem;
  z-index: 2; /* above particles */
}

.login-card {
  max-width: 400px;
  width: 100%;
  border: none;
  border-radius: 1rem;
  box-shadow: 0 4px 20px rgba(0,0,0,0.1);
  position: relative;
  z-index: 3; /* ensure card sits above the particles */
}

#particles-js {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 0; /* behind content */
  pointer-events: none; /* allow clicks through particles */
  background-repeat: no-repeat;
  background-size: cover;
}