betterCoolCardStyles.css

:host {
  font-family: sans-serif;
}

div.card {
  width: 100%;
  max-width: 300px;
  display: inline-block;
  box-shadow: 0px 1px 3px rgba(0, 0, 0, .6);
  margin: 10px;
  padding: 10px;
  background: white;
}

::slotted([slot="card-header"]) { /* use attribute selector */
  font-size: 25px;
  text-align: center;
}

::slotted([slot="card-body"]) {
  font-size: 20px;
}

::slotted([slot="card-author"]) {
  font-size: 14px;
  display: inline-block;
}

.card-footer {
  margin: 0px;
}