/* ========================================
   Design System & CSS Variables
   ======================================== */

:root {
    /* Light Theme Colors */
    --color-bg-primary: #f0f4f8;
    --color-bg-secondary: rgba(255, 255, 255, 0.85);
    --color-bg-card: rgba(255, 255, 255, 0.95);
    --color-text-primary: #1a202c;
    --color-text-secondary: #4a5568;
    --color-accent: hsl(220, 90%, 56%);
    --color-accent-hover: hsl(220, 90%, 48%);
    --color-gradient-1: hsl(280, 70%, 60%);
    --color-gradient-2: hsl(220, 90%, 56%);
    --color-gradient-3: hsl(180, 70%, 50%);

    /* Button Colors */
    --color-btn-number: rgba(255, 255, 255, 0.9);
    --color-btn-number-hover: rgba(255, 255, 255, 1);
    --color-btn-operator: hsl(220, 90%, 56%);
    --color-btn-operator-hover: hsl(220, 90%, 48%);
    --color-btn-function: rgba(255, 107, 107, 0.15);
    --color-btn-function-hover: rgba(255, 107, 107, 0.25);
    --color-btn-function-text: hsl(0, 70%, 60%);
    --color-btn-equals: hsl(140, 60%, 50%);
    --color-btn-equals-hover: hsl(140, 60%, 42%);

    /* Effects */
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.08);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.12);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.15);
    --shadow-glow: 0 0 24px rgba(66, 153, 225, 0.3);

    /* Spacing & Sizing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;

    --border-radius-sm: 0.5rem;
    --border-radius-md: 1rem;
    --border-radius-lg: 1.5rem;
    --border-radius-xl: 2rem;

    /* Transitions */
    --transition-fast: 0.15s ease;
    --transition-normal: 0.3s ease;
    --transition-slow: 0.5s ease;
}

/* Dark Theme */
body.dark-theme {
    --color-bg-primary: #0f172a;
    --color-bg-secondary: rgba(30, 41, 59, 0.85);
    --color-bg-card: rgba(30, 41, 59, 0.95);
    --color-text-primary: #f1f5f9;
    --color-text-secondary: #cbd5e1;
    --color-accent: hsl(220, 90%, 60%);
    --color-accent-hover: hsl(220, 90%, 68%);

    --color-btn-number: rgba(51, 65, 85, 0.9);
    --color-btn-number-hover: rgba(71, 85, 105, 1);
    --color-btn-operator: hsl(220, 90%, 60%);
    --color-btn-operator-hover: hsl(220, 90%, 68%);
    --color-btn-function: rgba(239, 68, 68, 0.2);
    --color-btn-function-hover: rgba(239, 68, 68, 0.3);
    --color-btn-function-text: hsl(0, 70%, 65%);
    --color-btn-equals: hsl(140, 60%, 55%);
    --color-btn-equals-hover: hsl(140, 60%, 63%);

    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.5);
    --shadow-glow: 0 0 24px rgba(96, 165, 250, 0.4);
}

/* ========================================
   Base Styles & Reset
   ======================================== */

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--color-bg-primary);
    color: var(--color-text-primary);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    overflow-x: hidden;
    transition: background var(--transition-normal), color var(--transition-normal);
}

/* ========================================
   Background & Animations
   ======================================== */

.background-gradient {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: -1;
    background: linear-gradient(135deg,
            var(--color-gradient-1) 0%,
            var(--color-gradient-2) 50%,
            var(--color-gradient-3) 100%);
    opacity: 0.15;
    animation: gradientShift 15s ease infinite;
}

@keyframes gradientShift {

    0%,
    100% {
        transform: scale(1) rotate(0deg);
        opacity: 0.15;
    }

    50% {
        transform: scale(1.1) rotate(5deg);
        opacity: 0.2;
    }
}

/* ========================================
   Container & Layout
   ======================================== */

.container {
    width: 100%;
    max-width: 900px;
    padding: var(--spacing-md);
}

.calculator-wrapper {
    display: flex;
    justify-content: center;
    align-items: center;
    animation: fadeInUp 0.6s ease;
}


@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* ========================================
   Calculator Component
   ======================================== */

.calculator {
    background: var(--color-bg-card);
    backdrop-filter: blur(20px);
    border-radius: var(--border-radius-xl);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-lg);
    border: 1px solid rgba(255, 255, 255, 0.2);
    width: 100%;
    max-width: 100%;
    transition: all var(--transition-normal);
}

.calculator:hover {
    box-shadow: var(--shadow-lg), var(--shadow-glow);
    transform: translateY(-2px);
}

/* Header */
.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-md);
}

.title {
    font-size: 1.75rem;
    font-weight: 700;
    background: linear-gradient(135deg, var(--color-gradient-1), var(--color-gradient-2));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.theme-toggle {
    width: 44px;
    height: 44px;
    border-radius: 50%;
    background: var(--color-btn-number);
    border: none;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-fast);
    position: relative;
}

.theme-toggle:hover {
    transform: rotate(180deg) scale(1.1);
    box-shadow: var(--shadow-md);
}

.theme-toggle:active {
    transform: rotate(180deg) scale(0.95);
}

.icon {
    width: 20px;
    height: 20px;
    color: var(--color-text-primary);
    transition: all var(--transition-fast);
    position: absolute;
}

.sun {
    opacity: 1;
}

.moon {
    opacity: 0;
}

body.dark-theme .sun {
    opacity: 0;
}

body.dark-theme .moon {
    opacity: 1;
}

/* Display */
.display-container {
    background: var(--color-bg-secondary);
    backdrop-filter: blur(10px);
    border-radius: var(--border-radius-md);
    padding: var(--spacing-md);
    margin-bottom: var(--spacing-md);
    min-height: 120px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    box-shadow: inset 0 2px 8px rgba(0, 0, 0, 0.1);
}

.display-history {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    min-height: 24px;
    text-align: right;
    margin-bottom: var(--spacing-xs);
    opacity: 0.7;
}

.display {
    font-size: 2.5rem;
    font-weight: 600;
    text-align: right;
    word-wrap: break-word;
    word-break: break-all;
    color: var(--color-text-primary);
    animation: textPulse 0.2s ease;
}

@keyframes textPulse {

    0%,
    100% {
        transform: scale(1);
    }

    50% {
        transform: scale(1.02);
    }
}

/* Buttons */
.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: var(--spacing-sm);
}

.btn {
    font-family: 'Inter', sans-serif;
    font-size: 1.25rem;
    font-weight: 500;
    height: 64px;
    border: none;
    border-radius: var(--border-radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    box-shadow: var(--shadow-sm);
    position: relative;
    overflow: hidden;
}

.btn::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.3);
    transform: translate(-50%, -50%);
    transition: width 0.6s, height 0.6s;
}

.btn:active::before {
    width: 300px;
    height: 300px;
}

.btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.btn:active {
    transform: translateY(0);
    box-shadow: var(--shadow-sm);
}

/* Button Types */
.btn-number {
    background: var(--color-btn-number);
    color: var(--color-text-primary);
}

.btn-number:hover {
    background: var(--color-btn-number-hover);
}

.btn-operator {
    background: var(--color-btn-operator);
    color: white;
    font-weight: 600;
}

.btn-operator:hover {
    background: var(--color-btn-operator-hover);
}

.btn-function {
    background: var(--color-btn-function);
    color: var(--color-btn-function-text);
    font-weight: 600;
}

.btn-function:hover {
    background: var(--color-btn-function-hover);
}

.btn-equals {
    background: var(--color-btn-equals);
    color: white;
    font-weight: 700;
    font-size: 1.5rem;
}

.btn-equals:hover {
    background: var(--color-btn-equals-hover);
}

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

/* ========================================
   Info Panel
   ======================================== */

.info-panel {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.info-card {
    background: var(--color-bg-card);
    backdrop-filter: blur(20px);
    border-radius: var(--border-radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-md);
    border: 1px solid rgba(255, 255, 255, 0.2);
    transition: all var(--transition-normal);
    animation: fadeInRight 0.6s ease 0.2s backwards;
}

.info-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
}

@keyframes fadeInRight {
    from {
        opacity: 0;
        transform: translateX(30px);
    }

    to {
        opacity: 1;
        transform: translateX(0);
    }
}

.info-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-sm);
    animation: bounce 2s ease-in-out infinite;
}

@keyframes bounce {

    0%,
    100% {
        transform: translateY(0);
    }

    50% {
        transform: translateY(-10px);
    }
}

.info-card h3 {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: var(--spacing-xs);
    color: var(--color-text-primary);
}

.info-card p {
    color: var(--color-text-secondary);
    line-height: 1.6;
}

.features {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: var(--spacing-sm);
}

.feature-item {
    background: var(--color-bg-card);
    backdrop-filter: blur(20px);
    border-radius: var(--border-radius-md);
    padding: var(--spacing-md);
    box-shadow: var(--shadow-sm);
    border: 1px solid rgba(255, 255, 255, 0.2);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-xs);
    transition: all var(--transition-normal);
    animation: fadeInRight 0.6s ease backwards;
}

.feature-item:nth-child(1) {
    animation-delay: 0.3s;
}

.feature-item:nth-child(2) {
    animation-delay: 0.4s;
}

.feature-item:nth-child(3) {
    animation-delay: 0.5s;
}

.feature-item:nth-child(4) {
    animation-delay: 0.6s;
}

.feature-item:hover {
    transform: translateY(-4px) scale(1.05);
    box-shadow: var(--shadow-md);
}

.feature-icon {
    font-size: 1.5rem;
}

.feature-text {
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--color-text-primary);
    text-align: center;
}

/* ========================================
   Responsive Design
   ======================================== */

@media (max-width: 767px) {
    .calculator {
        max-width: 100%;
    }

    .title {
        font-size: 1.5rem;
    }

    .display {
        font-size: 2rem;
    }

    .btn {
        height: 56px;
        font-size: 1.1rem;
    }

    .features {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 480px) {
    .container {
        padding: var(--spacing-sm);
    }

    .calculator {
        padding: var(--spacing-md);
    }

    .buttons {
        gap: var(--spacing-xs);
    }

    .btn {
        height: 52px;
        font-size: 1rem;
    }
}

/* ========================================
   Accessibility
   ======================================== */

.btn:focus-visible,
.theme-toggle:focus-visible {
    outline: 3px solid var(--color-accent);
    outline-offset: 2px;
}

@media (prefers-reduced-motion: reduce) {

    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}