style.css

body {
    background-color: #232323;
    margin: 0;
    font-family: 'Montserrat', sans-serif;
}

#container {
    max-width: 600px;
    margin: 20px auto;
}

/* 
padding-bottom is what makes the div a square block. Without it,
it is an empty element with no height. This following link helps 
understand why height is important.
https://stackoverflow.com/questions/5657964/css-why-doesn-t-percentage-height-work/5658062#5658062
 
height is based on the maximum height permitted by the element
and it's parent element. So, here 30% is the 30% of that maximum height.
It is not in reference to the maximum height/padding of the body. 
*/

.square{

    width: 30%;
    margin: 1.66%;
    background-color: purple;    
    float: left;
    padding-bottom: 30%;
    border-radius: 15%;

    transition: background-color 0.6s;
    -webkit-transition: background-color 0.6s;
    -o-transition: background-color 0.6s;

}

h1{
    text-align: center;
    color: white;
    background-color: steelblue;
    margin: 0;
    font-weight: normal;
    text-transform: uppercase;
    line-height: 1.1;
    padding: 20px 0;
}

button {
    border: none;
    background: none;
    text-transform: uppercase;
    height: 100%;
    color: steelblue;
    font-weight: bolder;
    letter-spacing: 1px;
    font-size: inherit;
    outline: none;

    /* Anytime a property changes on our button - color and background in 
    our case - it should take 1 sec to do that change. */

    transition: all 0.3s;
    -webkit-transition: all 0.3s;
    -o-transition: all 0.3s;
}

button:hover{
    color: white;
    background: steelblue;
}

/* We use display inline block with 20% of the total width to create 
spacing between buttons */
#message {
    display: inline-block;
    width: 20%;
}

#colorDisplay{
    font-size: 200%;
}

#stripe{
    background-color: white;
    height: 30px;
    text-align: center;
    color: black;
}

.selected{
    color: white;
    background: steelblue;
}