style.css

:root {
  --main-bg: white;
  --main-txt: black;
  --button-bg: black;
  --button-txt: white;
}

[data-theme="dark"] {
  --main-bg: black;
  --main-txt: white;
  --button-bg: white;
  --button-txt: black;
}

body {
  background-color: var(--main-bg);
  color: var(--main-txt);
}

button {
  background-color: var(--button-bg);
  color: var(--button-txt);
}

body {
  position: relative;
  min-width: 100vw;
  min-height: 100vh;
  display: flex;
  flex-flow: column;
  justify-content: center;
  align-items: center;
  font-family: 'Roboto', sans-serif;
  font-size: 16px;
  text-align: center;
}

body h1 {
  font-size: 3em;
  text-transform: uppercase;
  letter-spacing: 0.1em;
}

body button {
  border: 0;
  border-radius: 20px;
  padding: 10px 20px;
  letter-spacing: 0.1em;
  transition: all 0.3s;
  cursor: pointer;
  font-size: 1.1em;
}

body button:hover {
  opacity: 0.7;
}

body::after {
  position: absolute;
  bottom: 20px;
  color: var(--main-txt);
  font-size: 0.8em;
  content: 'MADE BY LUCIACENETIEMPO.COM';
  letter-spacing: 1px;
  width: 100%;
  text-align: center;
}