html, body {
  margin: 0;
  padding: 0;
  overflow-x: hidden;
}
* {
  box-sizing: border-box;
}
img {
  max-width: 100%;
  height: auto;
}
/* BOTÃO VOLTAR AO TOPO */
.btn_voltar_topo {
  position: fixed;
  right: 18px;
  bottom: 18px;
  width: 38px;
  height: 38px;
  border-radius: 50%;
  border: none;
  background: rgba(26, 62, 110, 0.82);
  color: #fff;
  font-size: 20px;
  font-weight: 700;
  cursor: pointer;
  display: none;
  align-items: center;
  justify-content: center;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.18);
  z-index: 999;
  opacity: 0.85;
}
.btn_voltar_topo:hover {
  opacity: 1;
  background: #1a3e6e;
}
.btn_voltar_topo.mostrar {
  display: flex;
}
body.modo-escuro .btn_voltar_topo {
  background: rgba(216, 163, 39, 0.9);
  color: #182230;
}