.header {
  margin-left: auto;
  margin-right: auto;
}

.header img {
  width: 600px;
  height: 300px;
  display: block;
  margin-left: auto;
  margin-right: auto;

}

body {
  background-color: #000;
}

.grid {
  width: 910px;
  margin-right: auto;
  margin-left: auto;
}

.gridlinks, .gridmidden, .gridrechts {
  float: left;
  width: 300px;

}

.gridmidden, .gridrechts {
  margin-left: 4px;
}

img {
  width: 300px;  
}

.overlay {
  
  height: 100%;
  width: 100%;
  opacity: 0;
  transition: .5s ease;
}

.container:hover .overlay {
  opacity: 1;
}

.text {
  color: white;
  font-size: 20px;
  position: absolute;
  top: 50%;
  left: 50%;
  -webkit-transform: translate(-50%, -50%);
  -ms-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
  text-align: center;
  font-family:'gill sans';
  font-style:oblique;
  background-color:rgba(210, 210, 210, 0.27);
  padding:10px;
  border-radius:10px;
  font-size:12px;
}
.container {
  position: relative;

}
.image {
  display: block;
  width: 100%;
  height: auto;
}
@media (max-width: 900px) {
  img {
    width: 400px;
  }
  .gridmidden, .gridrechts {
    float: none;
  }
  iframe {
    width: 400px;
  }
  .grid img{
    display: block;
    margin-left: auto;
    margin-right: auto;
  }
}