html {
 
  }

header {
    height: 100px;
    font-family: 'Rancho';
    font-size: 88px;
    background: #004643;
    color: #e8f5f2;
    padding: 0.2rem;
    text-align: center;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.26);
    width: 100%;
  }

  body {
 
    margin: 0;
  }
  
#calculator {
    font-family: 'Seven Segment', sans-serif;                                          
    font-size: 30px;
    margin: 1rem auto;
    width: 16rem;
    max-width: 90%;
    border: 1px solid #004643;
    border-radius: 10px;
    padding: 1rem;
    color: #001e1d;
  }

#calculator button {
    font: inherit; 
    background: #004643;
    color: #ffffff;
    border: 1px solid #004643;
    padding: 0.5rem;
    margin: 0.2rem;
    cursor: pointer;
    width: 70px;
    height: 70px;
  }

  #calculator button:focus {
    outline: none;
  }

#calculator button:hover,
#calculator button:active {
    background: #006f6a;
    border-color: #006f6a;
}

/* Neu für responsive   */

/* Sehr kleine Screens, z.B. iPhone */
@media (max-width: 430px) {
  header {
    font-size: 32px;   /* deutlich kleiner */
    height: auto;
    padding: 6px 4px;
  }

  #calculator {
    width: 12rem;      /* schmaler */
    max-width: 100%;
    margin: 0.5rem auto;
    padding: 0.5rem;
  }

  #calculator button {
    width: 48px;       /* viel kleinere Tasten */
    height: 48px;
    margin: 0.1rem;
    padding: 0.3rem;
  }
}