body {
    font-family: Arial, sans-serif;
    line-height: 1.6;
    margin: 0;
    padding: 0;
    background: #000000;
    color: #ffffff;
}

/* button */
.btn {
  margin: 100px;
  padding: 15px 40px;
  border: none;
  outline: none;
  color: #FFF;
  cursor: pointer;
  position: relative;
  z-index: 0;
  border-radius: 12px;
}
.btn::after {
  content: "";
  z-index: -1;
  position: absolute;
  width: 100%;
  height: 100%;
  background-color: #333;
  left: 0;
  top: 0;
  border-radius: 10px;
}
/* glow */
.btn::before {
  content: "";
  background: linear-gradient(
    45deg,
    #FF0000, #FF7300, #FFFB00, #48FF00,
    #00FFD5, #002BFF, #FF00C8, #FF0000
  );
  position: absolute;
  top: -2px;
  left: -2px;
  background-size: 600%;
  z-index: -1;
  width: calc(100% + 4px);
  height:  calc(100% + 4px);
  filter: blur(8px);
  animation: glowing 20s linear infinite;
  transition: opacity .3s ease-in-out;
  border-radius: 10px;
  opacity: 0;
}
@keyframes glowing {
  0% {background-position: 0 0;}
  50% {background-position: 400% 0;}
  100% {background-position: 0 0;}
}
/* hover */
.btn:hover::before {
  opacity: 1;
}
.btn:active:after {
  background: transparent;
}
.btn:active {
  color: #000;
  font-weight: bold;
}
header h1 {
    margin: 0;
}

nav ul {
    list-style: none;
    padding: 0;
}

nav ul li {
    display: inline;
    margin: 0 15px;
}

nav ul li a {
    color: #fff;
    text-decoration: none;
}

section {
    padding: 20px;
    margin: 0 auto;
    max-width: 800px;
}

section h2 {
    color: #FFFF00; /* Dark Blue */
}

section h3 {
    color: #FFFF00; /* Medium Blue */
}

article {
    margin-bottom: 20px;
}

footer {
    background: rgb(16,169,10); /* Even Darker Blue */
    color: #fff;
    text-align: center;
    padding: 1r 0;
    position: fixed;
    width: 0;
    bottom: 0;
}