.footer {
  width: 100%;
}
.header {
  width: 100%;
}
.main {
  flex-grow: 1;
}
.page {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  font-family: sans-serif;
  margin: 0;
  padding: 20px;
  box-sizing: border-box;
}
.footer__copyright {
  text-align: right;
}
.header_theme_dark {
  color: #fff;
}
.header__title {
  font-size: 3em;
}
.main__text {
  color: white;
}

.page__header {
  color: tomato;
}
.page_theme_dark {
  background-color: #000;
  color: #f5f5f5;
}