*{
   box-sizing: border-box;
   color: #fff;
}
body{
   margin: 0;
   padding: 0;
   min-height: 100vh;
   height: auto;
   background: #333;
}

#taschenrechner{
   position: absolute;
   min-width: 50%;
   top: 5%;
   left: 50%;
   transform: translate(-50%);
}

.text-field{
   width: 100%;
   margin-bottom: 0.5rem;
}
.text-field .long-field{
   padding: 1rem;
   border: 0.1rem solid #666;
   font-size: 1.2rem;
   outline: none;
   text-align: right;
   background: transparent;
   pointer-events: none;
   width: 100%;
}

.button-field{
   width: 100%;
   margin-bottom: 0.3rem;
   display: flex;
}
.button-field button{
   width: 25%;
   padding: 0.7rem;
   cursor: pointer;
   transition: 0.3s linear;
   border: none;
   outline: none;
   background: transparent;
}
.button-field .btn-number{
   background: #e74c3c;
}
.button-field .btn-number:hover{
   background: #e74c9c;
}

.button-field .btn-operator{
   background: navy;
}
.button-field .btn-operator:hover{
   background: #09e;
}

.button-field .btn-sum{
   background: green;
}
.button-field .btn-sum:hover{
   background: #00ff00;
}

.button-field .btn-reset{
   background: #cd3545;
}
.button-field .btn-reset:hover{
   background: red;
}