style.css

body {
  font-family: Söhne,ui-sans-serif,system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif,Helvetica Neue,Arial
}

/* Styling for the inputs */
fieldset {
  display: flex-wrap;
  flex-direction: row;
  border-radius: 11px;
  font-size: 1.9em;
}
input {
  width: 34vw;
  border-width: 1px;
  text-align: right;
  font-size: 2.5em;
  border-radius: 11px;
  caret-color: transparent;
}
input:disabled {
  background-color: white;
  color: black;
}
input:focus {
  background-color: #E9FFC9;
}
.flash {
  animation: 0.05s linear 5 alternate running fade-out;  
}
input::selection {
  background-color: #C9E9FF;
}
/* Chrome, Safari, Edge, Opera */
input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button {
  -webkit-appearance: none;
  margin: 0;
}
/* Firefox */
input[type=number] {
  -moz-appearance: textfield;
}

/* Styling for the buttons */
.buttons {
  display: flex;
  flex-wrap: wrap;
  width: 100%;
  background-color: #e8eaed;
}
.button {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 31vw;
  margin: 0.5vw;
  height: 2em;
  font-size: 3em;
  border: 1px solid #ddd;
  background-color: #ffffff;
  border-radius: 10px;
  box-shadow: 0px 2px #a9abad;
  cursor: pointer;
}

/* Styling for the "C" button */
.button.c {
  background: linear-gradient(#dd2222, #dd3322);
  border-radius: 10px;
  color: #ffffff;
  text-align: center;
  position: relative;
  background-image: linear-gradient(red,orangered);
  box-shadow: 0px 2px #cc0000;
}
.button.c:after{
  content: '';
  position: absolute;
  top: 2px;
  left: 2px;
  width: calc(100% - 4px);
  height: 50%;
  background: linear-gradient(rgba(255,255,255,0.8), rgba(255,255,255,0.2));
}

/* Media query for mobile devices */
@media (max-width: 768px) {
  .button {
    width: 100%;
    height: 75px;
    font-size: 2.5em;
  }
}
/* Add active effect */
.button:active {
  background-color: #ddd;
}
.button:focus {
  outline: none;
  box-shadow: none;
}

/* Styling for the bank-notes */
label { font-size: 2.5em; }

img.kovanica {
  border-radius: 50%;
}
img.novcanica {
  box-shadow:    2px 2px #D3D3D3;
}

@keyframes fade-out {
  from { 
    opacity: 0;
    background-color: orange;
  }
  to { 
    opacity: 1;
    background-color: orange;
  }
}