styles.css

.button {
    background-color: none;
    border-radius: 12px;
    border: 2px solid blue;
    opacity: 0.9;
    transition: 0.3s;
    color: blue;
    padding: 15px 32px;
    text-align: center;
    text-decoration: none;
    display: inline-block;
    font-size: 20px;
    margin-left: auto;
    margin-top: auto;
    cursor: pointer;
    width: auto;
    position: absolute;
}

body {
  display: flex;
  justify-content: center;
  width: 100%;
}

#svgMain {
  margin-left: auto;
  margin-right: auto;
}

.node {
  font: 300 11px "Helvetica Neue", Helvetica, Arial, sans-serif;
  fill: #bbb;
}

.node:hover {
  fill: #000;
}

.link {
  stroke: steelblue;
  stroke-opacity: 0.4;
  fill: none;
  pointer-events: none;
}

.node:hover,
.node--source,
.node--target {
  font-weight: 700;
}

.node--source {
  fill: #2ca02c;
}

.node--target {
  fill: #d62728;
}

.link--source,
.link--target {
  stroke-opacity: 1;
  stroke-width: 2px;
}

.link--source {
  stroke: #d62728;
}

.link--target {
  stroke: #2ca02c;
}