style.css

/* Variables */
:root {
  --bg-color: #000;
  --text-color: #fff;
  --btn-bg-light: #d0d0d0;
  --btn-bg-blue: #4b5efc;
  --btn-bg-dark: #2e2f38;
  --btn-bg-function: #a3a3a3;
  --input-bg: #1c1c1c;
  --btn-bg-scientific: #ff8c00;
  --accent-color: #ff8c00;
  --transition-duration: 0.3s;
}

body.light-theme {
  --bg-color: #f0f0f0;
  --text-color: #333;
  --btn-bg-light: #e0e0e0;
  --btn-bg-dark: #b0b0b0;
  --btn-bg-function: #f1f1f1;
  --input-bg: #e0e0e0;
  --btn-bg-scientific: #ff9e2c;
}

/* Base Styles */
body {
  height: 100vh;
  height: 100dvh;
  margin: 0;
  display: flex;
  flex-direction: column;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen-Sans, Ubuntu, Cantarell, 'Helvetica Neue', sans-serif;
  background-color: var(--bg-color);
  color: var(--text-color);
  transition: background-color var(--transition-duration), color var(--transition-duration);
}

/* Layout */
main {
  display: flex;
  flex-direction: column;
  height: 100%;
  max-height: 100vh;
  max-height: 100dvh;
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1), 0 1px 3px rgba(0, 0, 0, 0.08);
  border-radius: 12px;
  overflow: hidden;
}

section {
  display: flex;
  flex-wrap: wrap;
  flex: 1;
  padding: 10px;
  font-size: clamp(24px, 5vw, 40px);
  font-weight: 300;
}

/* Output Section */
#output {
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  align-items: flex-end;
  gap: 15px;
  position: relative;
  height: 150px;
  overflow: hidden;
}

#current, .row {
  display: flex;
  width: 100%;
}

#current {
  flex-direction: column;
}

/* Expression display */
#expression {
  text-align: right;
  font-size: clamp(24px, 4vw, 32px);
  color: var(--text-color);
  min-height: 30px;
  position: relative;
  vertical-align: middle;
  transition: all var(--transition-duration);
}

#expression::after {
  content: '|';
  animation: blink 1s step-end infinite;
  display: inline-block;
  margin-left: 2px;
  vertical-align: middle;
  margin-top: -10px;
}

#expression.has-content::after {
  display: none;
}

/* Result display */
#result {
  font-size: clamp(32px, 6vw, 48px);
  font-weight: bold;
  opacity: 0;
  position: absolute;
  bottom: 10px;
  right: 10px;
  transform: translateY(100%);
  transition: all var(--transition-duration);
  margin-top: 10px;
}

/* Input section */
#input {
  background-color: var(--input-bg);
  border-radius: 20px 20px 0 0;
  padding: 10px;
  margin-top: 10px;
  transition: background-color var(--transition-duration);
}

/* Buttons */
.btn {
  flex-basis: calc(25% - 10px);
  margin: 5px;
  font-size: clamp(18px, 4vw, 32px);
  height: 72px;
  border: 0;
  border-radius: 24px;
  cursor: pointer;
  color: var(--text-color);
  transition: background-color var(--transition-duration), transform 0.2s, color var(--transition-duration), filter var(--transition-duration);
}

.btn:active {
  transform: scale(0.95);
}

.btn:hover {
  filter: brightness(110%);
}

.btn:focus {
  outline: 2px solid var(--btn-bg-blue);
  outline-offset: 2px;
}

.btn:focus-visible {
  outline-color: var(--accent-color);
}

.btn.light { background-color: var(--btn-bg-light); }
.btn.blue { background-color: var(--btn-bg-blue); }
.btn.dark { background-color: var(--btn-bg-dark); }
.btn.function, .btn.operator { background-color: var(--btn-bg-function); }

.btn i {
  font-size: 1.2em;
}

/* Specific Button Styles */
.btn[data-action="decimal"] i {
  font-size: 0.5em;
  vertical-align: middle;
}

.btn[data-action="parenthesis"] {
  font-size: 1.2em;
  font-weight: 900;
}

.btn[data-action="clear"] {
  display: flex;
  justify-content: center;
  align-items: center;
}

.btn[data-action="clear"] i {
  font-size: 0.8em;
}

.btn[data-action="clear"] i + i {
  margin-left: 2px;
}

.btn[data-action="clear"] i.fa-a {
  font-size: 0.7em;
  opacity: 0.8;
}

.btn[data-action="clear"]:not(.all-clear) i.fa-a {
  display: none;
}

/* Scientific Buttons */
#scientific-buttons {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  width: 100%;
  transition: opacity var(--transition-duration) ease-in-out, max-height var(--transition-duration) ease-in-out;
  opacity: 0;
  max-height: 0;
  overflow: hidden;
}

#scientific-buttons.visible {
  opacity: 1;
  max-height: 500px;
}

#scientific-buttons .btn {
  height: 50px;
  font-size: 0.7em;
}

#scientific-buttons .row {
  display: flex;
  justify-content: space-between;
  width: 100%;
  margin-bottom: 2px;
}

.btn.scientific {
  font-size: 0.8em;
  padding: 0.5em;
}

.btn.function[data-action^="sin"],
.btn.function[data-action^="cos"],
.btn.function[data-action^="tan"],
.btn.function[data-action^="ln"],
.btn.function[data-action^="log"],
.btn.function[data-action^="e"],
.btn.function[data-action^="pi"],
.btn.function[data-action^="inv"],
.btn.function[data-action^="deg"],
#scientific-buttons .btn[data-action="factorial"] {
  background-color: var(--btn-bg-scientific);
  color: #fff;
}

#toggle-scientific {
  width: 100%;
  margin-bottom: 10px;
  display: flex;
  justify-content: center;
  align-items: center;
}

#toggle-scientific i {
  margin-right: 8px;
}

#toggle-scientific .toggle-text {
  display: inline;
}

/* Theme Toggle */
#theme-toggle {
  position: absolute;
  top: 10px;
  right: 10px;
  font-size: 40px;
  cursor: pointer;
  color: var(--text-color);
  z-index: 100;
  transition: color var(--transition-duration);
  background: none;
  border: none;
  padding: 0;
}

#theme-toggle:hover {
  color: var(--btn-bg-blue);
}

#theme-toggle:focus {
  outline: 2px solid var(--btn-bg-blue);
  outline-offset: 2px;
}

/* Animations */
@keyframes blink {
  0%, 100% { opacity: 1; }
  50% { opacity: 0; }
}

/* Responsive Design */
@media (min-width: 769px) {
  #scientific-buttons {
    display: flex;
  }
  
  #toggle-scientific.active {
    background-color: var(--btn-bg-blue);
    color: #fff;
  }
}

@media (max-width: 768px) {
  body {
    height: 100vh;
    height: -webkit-fill-available;
  }

  main {
    height: 100%;
    max-height: 100vh;
    max-height: -webkit-fill-available;
    border-radius: 0;
  }

  #toggle-scientific .toggle-text,
  #scientific-buttons .toggle-text {
    display: none;
  }

  #scientific-buttons.visible {
    display: flex;
  }
}

/* Accessibility */
@media (prefers-reduced-motion: reduce) {
  * {
    animation: none !important;
    transition: none !important;
  }
}