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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen,
    Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
  font-size: 16px;
  line-height: 1.618;
  display: flex;
  flex-flow: column nowrap;
  min-height: 100vh;
}

.header,
.main,
.footer {
  width: min(calc(100vw - 2rem), 350px);
  margin-left: auto;
  margin-right: auto;
}

.header,
.main {
  border: 3px solid hsl(219, 64%, 35%);
  border-radius: 5px;
  box-shadow: 2px 2px 0 0 hsl(219, 64%, 35%), 2px 2px 2px 0 hsl(219, 64%, 30%),
    3px 3px 3px 0 hsla(219, 64%, 25%, 0.65);
}

.header {
  background: hsl(219, 64%, 35%);
  border-bottom-left-radius: 0;
  border-bottom-right-radius: 0;
  color: hsl(0, 0%, 100%);
  margin-top: 2rem;
  padding: 0.5rem 1rem;
}

.branding {
  font-size: 1.5rem;
  font-variant: small-caps;
  letter-spacing: 1px;
  text-align: center;
  text-shadow: 1px 1px 0 hsl(0, 0%, 65%), 2px 2px 2px hsl(0, 0%, 0%);
}

.main {
  background: hsl(0, 0%, 97%);
  border-top-left-radius: 0;
  border-top-right-radius: 0;

  margin-bottom: 1rem;
}

.footer {
  font-size: 0.9rem;
  text-align: center;
  margin-top: auto;
  padding: 1rem 0;
}

.calculator {
  padding: 1rem;
}

.calculator__display {
  background: hsl(0, 0%, 100%);
  border: 1px solid hsl(0, 0%, 60%);
  border-radius: 2px;
  box-shadow: inset 0 0 2px 0 hsl(0, 0%, 70%), 0 0 0 1px hsl(0, 0%, 75%);
  font-size: clamp(2rem, 3vw, 2.5rem);
  font-weight: 600;
  text-align: right;
  width: 100%;
  margin-bottom: 1rem;
  padding: 0.2rem 1rem;
}

.calculator__entry-pad {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: 1fr 6fr;
  gap: 1rem;
  justify-items: end;
}

.calculator__clear {
  grid-column: 3 / 5;
  grid-row: 1;
  display: flex;
  flex-flow: row nowrap;
  justify-content: flex-end;
  gap: 1rem;
}

.calculator__digits {
  grid-column: 1 / 4;
  grid-row: 2;
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1rem;
}

.calculator__operations {
  grid-column: 4;
  grid-row: 2;
  display: flex;
  flex-flow: column nowrap;
  gap: 1rem;
}

.btn {
  display: block;
  padding: clamp(0.1rem, 5vw, 0.3rem) clamp(1rem, 6vw, 1.5rem);
  background: hsl(0, 0%, 95%);
  border: 1px solid hsl(0, 0%, 85%);
  border-radius: 3px;
  box-shadow: 0 0 2px hsl(0, 0%, 80%), 0 0 0 2px hsl(0, 0%, 60%),
    1px 1px 0 3px hsl(0, 0%, 50%);
  font-family: inherit;
  font-size: inherit;
  line-height: inherit;
  cursor: pointer;
  transition: all 0.15s ease-in-out 0s;
}

.btn:hover,
.btn:focus {
  background: hsl(0, 0%, 100%);
}

.btn:focus {
  outline: 3px solid hsl(219, 64%, 35%);
}

.btn:active {
  background: hsl(0, 0%, 90%);
  box-shadow: 0 0 0 hsl(0, 0%, 80%), 0 0 0 2px hsl(0, 0%, 80%),
    0 0 0 3px hsl(0, 0%, 50%);
  outline: none;
  transform: translateX(2px) translateY(2px) scale(0.96);
}