* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh; /*100% da altura */
  width: 100vw; /*100% da largura */
  background-color:#111;
}

.clock {
  position: relative;
  width: 250px;
  height: 250px;
  border: 7px solid #333;
  border-radius: 50%;
  display: flex;
  justify-content: center;
  align-items: center;
  background: url(imagem/mostrador-250.png) no-repeat;

}

.hour, 
.minute, 
.second {
  position: absolute; 
/*  background-color: #333; */
  border-radius: 6px;
  transform-origin: 50% 100%;	
}

.hour {
  height: 75px;
  width: 5px;
  background-color: #000;
  bottom:50%;
  left:50%;  
}

.minute {
  height: 80px;
  width: 4px;
  background-color: #fda800;
  bottom:50%;
  left:50%;
}

.second {
  height: 86px;
  width: 2px;
  background-color: #f00;
  bottom:50%;
  left:50%;
}

.center {
  position: absolute;
  width: 15px;
  height: 15px;
  background-color: #333;
  border-radius: 50%;
}

.digital-time {
  position: absolute;
  bottom:145px;
  font-size: 18px;
  font-family: Arial, sans-serif;
  color: #000;
}
/*==================================================================
    A inserção do simples comando abaixo, no código css, já torna as
    imagens flexiveis
    =================================================================*/
    img{
      max-width: 100%; /* define a largura máxima em até 100% */
  }