css
@charset "UTF-8";

body {
  background-color: #fff;
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
}

body * {
  box-sizing: border-box;
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
}

#container {
  background: #333;
  border: 4px solid #000;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
  padding: 20px;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 80%;
  height: 80%;
}

h1 {
  background: #fff;
  border: 4px solid #000;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
  font-size: 24px;
  letter-spacing: 1px;
  margin: 0;
  padding: 10px;
  text-align: center;
  width: 100%;
}

h1 > span {
  background: #fff;
  border: 4px solid #000;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
  font-size: 24px;
  letter-spacing: 1px;
  margin: 0;
  padding: 10px;
  text-align: left;
  width: auto;
}

h2 {
  background: #fff;
  border: 4px solid #000;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
  font-size: 18px;
  letter-spacing: 1px;
  margin: 0;
  padding: 10px;
  text-align: center;
  width: 100%;
  text-transform: uppercase;
}

h3 {
  background: #fff;
  border: 4px solid #000;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
  font-size: 14px;
  letter-spacing: 1px;
  margin: 0;
  padding: 10px;
  text-align: left;
  width: auto;
}

p {
  background: #fff;
  border: 4px solid #000;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
  line-height: 1.2;
  margin: 0;
  padding: 20px;
  text-align: left;
  width: 100%;
}

span {
  background: #fff;
  border: 4px solid #000;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
  font-size: 12px;
  letter-spacing: 1px;
  margin: 0 10px 0 0;
  padding: 10px;
  text-align: left;
  width: auto;
}

a {
  text-decoration: none;
  color: #000;
  background: #f00;
  padding: 10px 20px;
  border: 4px solid #000;
  border-radius: 0;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
  text-align: center;
  display: inline-block;
  width: 100%;
  font-size: 12px;
  letter-spacing: 1px;
  margin: 10px;
  background-image: linear-gradient(90deg, #000, #000);
  background-size: 100% 100%;
  background-position: 0 0;
  background-clip: border-box;
  transition: background 1s;
}

a:hover {
  background: #f00;
  color: #000;
  text-decoration: none;
  background-size: 100% 100%;
  background-position: 0 0;
  background-clip: border-box;
  transition: background 1s;
}