style.css

body {
  background: #1d1d1d;
  box-shadow: 0 0 3px rgba(0, 0, 0, 0.1);
  border-radius: 20px;
  -webkit-border-radius: 20px;
  -moz-border-radius: 20px;
}

h1 {
  font-family: Helvetica, Arial, sans-serif;
  color: #a4aeff;
  text-align: center;
  text-transform: uppercase;
  font-size: 22px;
  font-weight: normal;
  border-top-left-radius: 20px;
  border-top-right-radius: 20px;
}

p {
  font-family: Helvetica, Arial, sans-serif;
  padding-left: 20px;
  color: white;
  text-align: center;
}

summary {
  font-size: 11px;
  text-align: center;
}

details {
  font-family: Helvetica, Arial, sans-serif;
  padding-left: 20px;
  color: white;
  text-align: left;
  font-size: 14px;
}

button {
  text-transform: uppercase;
  font-weight: bold;
  display: block;
  margin: 30px auto;
  background: #a4aeff;
  border-radius: 5px;
  width: 200px;
  height: 50px;
  font-size: 17px;
  color: white;
}

button:hover {
  background: #76bb40;
  border-bottom-color: #111;
}

button:active {
  position: relative;
  top: 1px;
}

#replace, #regex, #text {
  font-size: 14px;
  color: black;
  background-color: #f7f7f7;
  width: 60%;
  padding: 5px 5px 8px 8px;
}

#flags {
  padding: 10px 10px 15px 15px;
  margin-left: 5px;
  font-size: 15px;
}

small {
  font-family: Helvetica, Arial, sans-serif;
  padding-left: 10px;
  color: gray;
  text-align: center;
}

a:link, a:clicked {
  color: lightskyblue;
}

a:hover, a:active {
  color: lightblue;
}

footer {
  font-family: Helvetica, Arial, sans-serif;
  padding-left: 10px;
  color: gray;
  text-align: center;
  font-size: 12px;
}

code {
  font-family: Monaco, monospace;
  color: lightgray;
}