style.css

body,html {
  width: 100%;
  height: 100%;
  font-family: 'Montserrat', sans-serif;
   background: url(https://wallpaperaccess.com/full/415831.jpg) no-repeat center center fixed; 
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;

}



.title{
	font-family: 'Gochi Hand', cursive;
	/*margin: 20px;*/
	color: #ffff00;
	font-size: 4em;
}

h1{
	font-size: 4em;
	color: 
}


a{
	padding: 70px 0;
	text-align: center;
	font-size: 18px;
}


a:link {
  color: #ffff00;
   text-decoration: none;
}

/* visited link */
a:visited {
  color: #ffff00;
   text-decoration: none;
}

/* mouse over link */
a:hover {
  	color:white;
	 text-decoration: none;
}

/* selected link */
a:active {
  color: red;
   text-decoration: none;
}

.img{
	height: 170px;
  width: 170px;
  border-radius: 10%;
	margin-right: 50px;
	
	color: #ffff00;
	background-color: silver;
	border :none;
	transition: all 1s;
}

.img:hover{
	transform: scale(1.3);
	color: #ffff00;
}

.imgAGN{
                background: url(AGN.jpg) no-repeat;
                background-size: 100%;
                cursor:pointer;
             
            }

.imgStars{
                background: url(https://vignette.wikia.nocookie.net/newdcmovieuniverse/images/3/37/El-sol.jpg/revision/latest?cb=20131023220054) no-repeat;
                
                background-size: 100%;
                cursor:pointer;
                
            }

.imgPlanets{
                background: url(Planet.jpg) no-repeat;
               background-size: 100%;
                cursor:pointer;
                
            }

.imgClusters{

 background: url(https://science.nasa.gov/science-red/s3fs-public/styles/image_gallery_scale_960w/public/atoms/m13s_3Block.jpg?itok=hWACEusA) no-repeat;
               background-size: 100%;
                cursor:pointer;
}

.imgGalaxies{
 background: url(https://upload.wikimedia.org/wikipedia/commons/c/c4/Blackeyegalaxy.jpg) no-repeat;
               background-size: 100%;
                cursor:pointer;
}


.container {
 /*width:950px;*/
 display: flex;
justify-content: space-between;

text-align: center;	
}

.center{
	padding: 70px 0;
	text-align: center;
}