/* ===================================
   CSS Variables & Reset
   =================================== */

:root {
    /* Color Palette - Scientific Precision */
    --color-bg: #faf9f6;
    --color-bg-card: #ffffff;
    --color-text: #2c2c2c;
    --color-text-muted: #6b6b6b;
    --color-border: #d4d4d4;
    --color-border-light: #e8e8e8;

    /* Accent Colors - Calculator Inspired */
    --color-primary: #f57c00;      /* Amber/Orange */
    --color-primary-dark: #e65100;
    --color-primary-light: #ff9800;
    --color-secondary: #455a64;     /* Blue-gray */
    --color-success: #43a047;       /* Green */

    /* Typography */
    --font-display: 'Archivo', sans-serif;
    --font-body: 'DM Sans', sans-serif;
    --font-mono: 'DM Mono', monospace;

    /* Spacing - Mathematical precision */
    --spacing-unit: 8px;
    --spacing-xs: calc(var(--spacing-unit) * 1);
    --spacing-sm: calc(var(--spacing-unit) * 2);
    --spacing-md: calc(var(--spacing-unit) * 3);
    --spacing-lg: calc(var(--spacing-unit) * 4);
    --spacing-xl: calc(var(--spacing-unit) * 6);
    --spacing-2xl: calc(var(--spacing-unit) * 8);

    /* Effects */
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.06);
    --shadow-md: 0 2px 8px rgba(0, 0, 0, 0.08);
    --shadow-lg: 0 4px 16px rgba(0, 0, 0, 0.1);
    --shadow-focus: 0 0 0 3px rgba(245, 124, 0, 0.2);

    --transition: 0.2s cubic-bezier(0.4, 0, 0.2, 1);

    /* Border Radius */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
}

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

html {
    font-size: 16px;
}

body {
    font-family: var(--font-body);
    background: var(--color-bg);
    color: var(--color-text);
    line-height: 1.6;
    overflow-x: hidden;
    min-height: 100vh;
    position: relative;
}

/* ===================================
   Geometric Background
   =================================== */

.geo-background {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 0;
    pointer-events: none;
    opacity: 0.04;
}

.geo-circle {
    position: absolute;
    top: 10%;
    right: 10%;
    width: 300px;
    height: 300px;
    border: 2px solid var(--color-primary);
    border-radius: 50%;
    animation: float 20s ease-in-out infinite;
}

.geo-square {
    position: absolute;
    bottom: 15%;
    left: 5%;
    width: 200px;
    height: 200px;
    border: 2px solid var(--color-secondary);
    transform: rotate(45deg);
    animation: float 25s ease-in-out infinite reverse;
}

.geo-triangle {
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-left: 150px solid transparent;
    border-right: 150px solid transparent;
    border-bottom: 260px solid var(--color-primary);
    opacity: 0.5;
    animation: float 30s ease-in-out infinite;
}

@keyframes float {
    0%, 100% {
        transform: translateY(0) rotate(0deg);
    }
    50% {
        transform: translateY(-30px) rotate(180deg);
    }
}

/* ===================================
   Container
   =================================== */

.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
    position: relative;
    z-index: 2;
}

/* ===================================
   Header
   =================================== */

.header {
    padding: var(--spacing-xl) 0 var(--spacing-lg);
    text-align: center;
}

.logo {
    display: inline-flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-sm);
}

.logo-symbol {
    position: relative;
    width: 60px;
    height: 60px;
    background: var(--color-primary);
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: var(--shadow-lg);
    overflow: hidden;
}

.symbol-line {
    position: absolute;
    width: 30px;
    height: 3px;
    background: #fff;
}

.symbol-line:nth-child(1) {
    top: 18px;
}

.symbol-line:nth-child(2) {
    bottom: 18px;
}

.symbol-equal {
    font-size: 24px;
    font-weight: 700;
    color: #fff;
    font-family: var(--font-mono);
}

.logo-text h1 {
    font-family: var(--font-display);
    font-size: 2rem;
    font-weight: 700;
    color: var(--color-text);
    letter-spacing: -0.5px;
}

.subtitle {
    font-size: 0.875rem;
    color: var(--color-text-muted);
    font-weight: 500;
}

/* ===================================
   Main Card
   =================================== */

.main-card {
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
    padding: var(--spacing-xl);
    margin-bottom: var(--spacing-lg);
}

/* ===================================
   Section Titles
   =================================== */

.section-title {
    font-family: var(--font-display);
    font-size: 0.875rem;
    font-weight: 700;
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 1px;
    margin-bottom: var(--spacing-md);
}

/* ===================================
   Category Grid
   =================================== */

.category-section {
    margin-bottom: var(--spacing-xl);
    padding-bottom: var(--spacing-xl);
    border-bottom: 1px solid var(--color-border-light);
}

.category-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--spacing-sm);
}

.category-btn {
    padding: var(--spacing-md);
    background: var(--color-bg);
    border: 2px solid var(--color-border);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-xs);
    font-family: var(--font-body);
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--color-text);
}

.category-btn i {
    font-size: 1.25rem;
    color: var(--color-text-muted);
    transition: all var(--transition);
}

.category-btn:hover {
    border-color: var(--color-primary);
    background: var(--color-bg-card);
    transform: translateY(-2px);
    box-shadow: var(--shadow-sm);
}

.category-btn:hover i {
    color: var(--color-primary);
}

.category-btn.active {
    background: var(--color-primary);
    border-color: var(--color-primary);
    color: #fff;
    box-shadow: var(--shadow-md);
}

.category-btn.active i {
    color: #fff;
}

/* ===================================
   Conversion Section
   =================================== */

.conversion-section {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    gap: var(--spacing-lg);
    align-items: center;
    margin-bottom: var(--spacing-xl);
}

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

.panel-label {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.input-group {
    display: flex;
    gap: var(--spacing-sm);
}

.value-input {
    flex: 1;
    padding: var(--spacing-md);
    font-family: var(--font-mono);
    font-size: 1.5rem;
    font-weight: 500;
    background: var(--color-bg);
    border: 2px solid var(--color-border);
    border-radius: var(--radius-md);
    color: var(--color-text);
    transition: all var(--transition);
    text-align: right;
}

.value-input:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: var(--shadow-focus);
}

.value-input::placeholder {
    color: var(--color-text-muted);
    opacity: 0.4;
}

/* Remove spinner arrows */
.value-input::-webkit-outer-spin-button,
.value-input::-webkit-inner-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

.value-input[type=number] {
    -moz-appearance: textfield;
}

.result-display {
    flex: 1;
    padding: var(--spacing-md);
    font-family: var(--font-mono);
    font-size: 1.5rem;
    font-weight: 500;
    background: linear-gradient(135deg, #fff8e1, #ffe0b2);
    border: 2px solid var(--color-primary);
    border-radius: var(--radius-md);
    color: var(--color-primary-dark);
    text-align: right;
    display: flex;
    align-items: center;
    justify-content: flex-end;
    box-shadow: var(--shadow-sm);
    user-select: all;
}

.unit-select {
    padding: var(--spacing-md);
    font-family: var(--font-body);
    font-size: 0.9375rem;
    font-weight: 600;
    background: var(--color-bg-card);
    border: 2px solid var(--color-border);
    border-radius: var(--radius-md);
    color: var(--color-text);
    cursor: pointer;
    transition: all var(--transition);
    min-width: 120px;
}

.unit-select:hover {
    border-color: var(--color-primary);
}

.unit-select:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: var(--shadow-focus);
}

/* ===================================
   Swap Button
   =================================== */

.swap-container {
    display: flex;
    align-items: center;
    justify-content: center;
}

.swap-btn {
    width: 48px;
    height: 48px;
    background: var(--color-bg-card);
    border: 2px solid var(--color-border);
    border-radius: 50%;
    cursor: pointer;
    transition: all var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--color-text-muted);
    font-size: 1.125rem;
}

.swap-btn:hover {
    background: var(--color-primary);
    border-color: var(--color-primary);
    color: #fff;
    transform: rotate(180deg);
    box-shadow: var(--shadow-md);
}

.swap-btn:active {
    transform: rotate(180deg) scale(0.95);
}

/* ===================================
   Action Buttons
   =================================== */

.actions-section {
    display: grid;
    grid-template-columns: 2fr 1fr;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-lg);
}

.btn {
    padding: var(--spacing-md) var(--spacing-lg);
    font-family: var(--font-body);
    font-size: 1rem;
    font-weight: 600;
    border: 2px solid var(--color-border);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition);
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
}

.btn:hover {
    transform: translateY(-1px);
    box-shadow: var(--shadow-sm);
}

.btn:active {
    transform: translateY(0);
}

.btn-primary {
    background: var(--color-primary);
    border-color: var(--color-primary);
    color: #fff;
    box-shadow: var(--shadow-sm);
}

.btn-primary:hover {
    background: var(--color-primary-dark);
    border-color: var(--color-primary-dark);
    box-shadow: var(--shadow-md);
}

.btn-secondary {
    background: var(--color-bg-card);
    border-color: var(--color-border);
    color: var(--color-text);
}

.btn-secondary:hover {
    border-color: var(--color-secondary);
    background: var(--color-bg);
}

/* ===================================
   Formula Section
   =================================== */

.formula-section {
    padding: var(--spacing-md);
    background: #f5f5f5;
    border-left: 4px solid var(--color-primary);
    border-radius: var(--radius-sm);
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

.formula-label {
    font-size: 0.75rem;
    font-weight: 700;
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 0.5px;
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
}

.formula-label i {
    color: var(--color-primary);
}

.formula-display {
    font-family: var(--font-mono);
    font-size: 0.875rem;
    color: var(--color-text);
    font-weight: 500;
}

/* ===================================
   Quick Conversions
   =================================== */

.quick-conversions {
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
    padding: var(--spacing-lg);
    margin-bottom: var(--spacing-xl);
}

.quick-title {
    font-family: var(--font-display);
    font-size: 1rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: var(--spacing-md);
}

.quick-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: var(--spacing-sm);
}

.quick-item {
    padding: var(--spacing-sm);
    background: var(--color-bg);
    border: 1px solid var(--color-border-light);
    border-radius: var(--radius-sm);
    font-family: var(--font-mono);
    font-size: 0.8125rem;
    color: var(--color-text);
    text-align: center;
    transition: all var(--transition);
}

.quick-item:hover {
    border-color: var(--color-primary);
    background: var(--color-bg-card);
}

/* ===================================
   Footer
   =================================== */

.footer {
    padding: var(--spacing-lg) 0 var(--spacing-xl);
    text-align: center;
    border-top: 1px solid var(--color-border-light);
}

.footer p {
    font-size: 0.875rem;
    color: var(--color-text-muted);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-xs);
}

.footer i {
    color: var(--color-primary);
}

/* ===================================
   Toast
   =================================== */

.toast {
    position: fixed;
    bottom: var(--spacing-lg);
    left: 50%;
    transform: translateX(-50%) translateY(150%);
    background: var(--color-text);
    color: #fff;
    padding: var(--spacing-md) var(--spacing-xl);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-lg);
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-size: 0.9375rem;
    font-weight: 600;
    z-index: 1000;
    transition: transform var(--transition);
}

.toast.show {
    transform: translateX(-50%) translateY(0);
}

.toast i {
    color: var(--color-success);
    font-size: 1.125rem;
}

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

@media (max-width: 768px) {
    .category-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .conversion-section {
        grid-template-columns: 1fr;
        gap: var(--spacing-md);
    }

    .swap-container {
        order: 2;
    }

    .swap-btn {
        transform: rotate(90deg);
    }

    .swap-btn:hover {
        transform: rotate(270deg);
    }

    .actions-section {
        grid-template-columns: 1fr;
    }

    .quick-grid {
        grid-template-columns: 1fr;
    }

    .input-group {
        flex-direction: column;
    }

    .unit-select {
        width: 100%;
    }
}

@media (max-width: 480px) {
    .logo-text h1 {
        font-size: 1.5rem;
    }

    .category-grid {
        grid-template-columns: 1fr;
    }

    .value-input,
    .result-display {
        font-size: 1.25rem;
    }
}

/* ===================================
   Utilities
   =================================== */

.hidden {
    display: none !important;
}

/* Selection */
::selection {
    background: var(--color-primary-light);
    color: #fff;
}

::-moz-selection {
    background: var(--color-primary-light);
    color: #fff;
}