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

body {
  background-color: #1e1e2f;
  color: white;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  transition: background-color 0.3s, color 0.3s;
}

body.light-mode {
  background-color: #f5f5f5;
  color: #1e1e2f;
}

.calculator {
  display: grid;
  grid-template-rows: minmax(80px, auto) repeat(5, 60px);
  grid-template-columns: repeat(4, 60px);
  justify-content: center;
  background-color: #1e1e2f;
  padding: 1.4rem;
  border-radius: 12px;
  gap: 1rem;
  max-width: 350px;
  border: 1px solid hsl(230, 6%, 40%);
}

body.light-mode .calculator {
  background-color: #f5f5f5;
  border-color: #ccc;
}

.calculator button {
  border: none;
  font-size: 1.3rem;
  font-weight: 500;
  color: white;
  background-color: hsl(230, 6%, 20%);
  border-radius: 10px;
  cursor: pointer;
  transition: background-color 0.2s;
  padding: 10px;
}

.calculator button:hover {
  background-color: hsl(230, 6%, 30%);
}

body.light-mode .calculator button {
  background-color: #e2e2e2;
  color: #1e1e2f;
}

body.light-mode .calculator button:hover {
  background-color: #cfcfcf;
}

.span-2 {
  grid-column: span 2;
}

.output {
  font-size: 2rem;
  background-color: #1e1e2f;
  color: white;
  grid-column: 1 / -1;
  display: flex;
  flex-direction: column;
  justify-content: space-around;
  align-items: flex-end;
  word-break: break-word;
  padding: 0.5rem;
  border-radius: 10px;
  border: 1px solid hsl(230, 6%, 40%);
}

body.light-mode .output {
  background-color: #f5f5f5;
  color: #1e1e2f;
  border-color: #ccc;
}

.prev-display {
  font-size: 1.2rem;
  font-weight: 400;
  color: white;
}

body.light-mode .prev-display {
  color: #1e1e2f;
}

.history-panel {
  background-color: hsl(230, 6%, 20%);
  color: white;
  padding: 1rem;
  border-radius: 10px;
  margin: 1rem auto;
  max-width: 350px;
  border: 1px solid hsl(230, 6%, 40%);
}

body.light-mode .history-panel {
  background-color: #e2e2e2;
  color: #1e1e2f;
  border-color: #ccc;
}

.history-list {
  max-height: 200px;
  overflow-y: auto;
  padding-left: 0;
  list-style-type: none;
  margin-top: 10px;
}

.history-list li {
  padding: 0.5rem;
  border-bottom: 1px solid hsl(230, 6%, 40%);
  font-size: 0.95rem;
  color: white;
}

body.light-mode .history-list li {
  color: black !important;
  border-color: #000000 !important; 
}

.d-none {
  display: none !important;
}

@media (max-width: 500px) {
  .calculator {
    grid-template-columns: repeat(4, 1fr);
    max-width: 90vw;
    padding: 1rem;
  }

  .calculator button {
    font-size: 1.1rem;
  }
}