.gallery-modal {
    position: fixed; /* wichtig: über gesamte Seite */
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    background: rgba(0,0,0,0.9);
    display: none;
    align-items: center;
    justify-content: center;
    z-index: 10000;
}
.gallery-modal img {
    max-width: 90%;
    max-height: 90%;
	position:absolute;
	  top: 50%;
  left: 50%;
  -ms-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
}
.gallery-modal .close-btn,
.gallery-modal .nav-btn {
    position: absolute;
    color: white;
    background: rgba(0,0,0,0.4);
    border: none;
    cursor: pointer;
    font-size: 2rem;
    padding: 0.5rem 1rem;
}
.gallery-modal .close-btn {
    top: 10px;
    right: 10px;
}
.gallery-modal .nav-btn.left {
    left: 10px;
    top: 50%;
    transform: translateY(-50%);
}
.gallery-modal .nav-btn.right {
    right: 10px;
    top: 50%;
    transform: translateY(-50%);
}