style.css

html, body {
  height: 100%;
  width: 100%;
  background-color: #d2ecf4;
}

img {
/*   height: 40%;
  width: 40%; */
  margin-left: 120px;
  margin-right: auto;
}

input {
  width: 50px;
}

h1 {
  width: 60%;
  color:#59599b;
  background:white;
  border: solid 12px;
  padding:30px;
  text-align: center;
  margin: 30px auto;
}

.instructions {
  font-style: calibri;
  background: white;
  padding: 10px;
  margin: 0 auto;
  margin-top: 10px;
  border: solid 2px black;
  width: 1100px;
  border-radius: 10px;
  font-size: 1.2em;
}
.paddingExtra {
  padding: 20px;
}

button {
  background-color: orange;
  padding: 7px;
  font: helvetica;
  color: white;
}

.center {
  text-align: center;
}


@media (max-width: 1200px) {
  .instructions{
    width: 900px;
  }
  img {
    width: 90%;
    margin-left: 40px;
  }
}

@media (max-width: 992px) {
  .instructions{
    width: 90%;
  }
  h3 {
    width:auto
  }
}

@media (max-width: 768px) {
  img {
    width: 80%;
  }
  .instructions{
    width:85%;
    margin:0 auto;
    border: none;
    margin-top: 20px;
  }
  body{
    margin:0;
    padding:0;
  }
  h1 {
    font-size:2em;
  }
}

.matrix {
  position: relative;
  margin-left: auto;
  margin-right: auto;
}
.matrix:before, .matrix:after {
    content: "";
    position: absolute;
    top: 0;
    border: 1px solid #000;
    width: 6px;
    height: 100%;
}
.matrix:before {
    left: -6px;
    border-right: 0;
}
.matrix:after {
    right: -6px;
    border-left: 0;
}