/* ===== CSS Variables & Design Tokens ===== */
:root {
    /* Colors */
    --primary-gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --secondary-gradient: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    --success-gradient: linear-gradient(135deg, #11998e 0%, #38ef7d 100%);
    --accent-gradient: linear-gradient(135deg, #fc466b 0%, #3f5efb 100%);

    --bg-primary: #0f0f1a;
    --bg-secondary: #1a1a2e;
    --bg-card: rgba(30, 30, 50, 0.8);
    --bg-glass: rgba(255, 255, 255, 0.05);

    --text-primary: #ffffff;
    --text-secondary: rgba(255, 255, 255, 0.7);
    --text-muted: rgba(255, 255, 255, 0.5);

    --border-color: rgba(255, 255, 255, 0.1);
    --border-glow: rgba(102, 126, 234, 0.5);

    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;

    /* Border Radius */
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 24px;
    --radius-full: 9999px;

    /* Shadows */
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.2);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.4);
    --shadow-glow: 0 0 40px rgba(102, 126, 234, 0.3);

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

/* ===== Reset & Base Styles ===== */
*,
*::before,
*::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    line-height: 1.6;
    overflow-x: hidden;
}

body::before {
    content: '';
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: radial-gradient(circle at 20% 20%, rgba(102, 126, 234, 0.15) 0%, transparent 40%),
    radial-gradient(circle at 80% 80%, rgba(118, 75, 162, 0.15) 0%, transparent 40%),
    radial-gradient(circle at 50% 50%, rgba(240, 147, 251, 0.05) 0%, transparent 60%);
    pointer-events: none;
    z-index: 0;
}

/* ===== App Container ===== */
.app-container {
    position: relative;
    z-index: 1;
    max-width: 800px;
    margin: 0 auto;
    padding: var(--spacing-xl);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* ===== Header ===== */
.header {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
    animation: fadeInDown 0.6s ease;
}

.logo {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-sm);
}

.logo-icon {
    width: 48px;
    height: 48px;
    color: #667eea;
    filter: drop-shadow(0 0 10px rgba(102, 126, 234, 0.5));
}

.header h1 {
    font-size: 2.5rem;
    font-weight: 700;
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.02em;
}

.subtitle {
    color: var(--text-secondary);
    font-size: 1.1rem;
    font-weight: 400;
}

/* ===== Main Content ===== */
.main-content {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xl);
}

/* ===== Mode Selector ===== */
.mode-selector {
    animation: fadeIn 0.6s ease 0.1s both;
}

.mode-selector h2 {
    font-size: 1rem;
    font-weight: 500;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
    text-align: center;
}

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

.mode-btn {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-lg);
    background: var(--bg-glass);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    cursor: pointer;
    transition: all var(--transition-normal);
    backdrop-filter: blur(10px);
}

.mode-btn:hover {
    background: rgba(255, 255, 255, 0.08);
    border-color: rgba(102, 126, 234, 0.3);
    transform: translateY(-2px);
}

.mode-btn.active {
    background: linear-gradient(135deg, rgba(102, 126, 234, 0.2) 0%, rgba(118, 75, 162, 0.2) 100%);
    border-color: rgba(102, 126, 234, 0.5);
    box-shadow: var(--shadow-glow);
}

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

.mode-label {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
}

.mode-desc {
    font-size: 0.75rem;
    color: var(--text-muted);
}

/* ===== Calculator Card ===== */
.calculator-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    backdrop-filter: blur(20px);
    box-shadow: var(--shadow-lg);
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xl);
    animation: fadeIn 0.6s ease 0.2s both;
}

/* ===== Input Groups ===== */
.input-group {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
    transition: all var(--transition-normal);
}

.input-group.hidden {
    display: none;
}

.input-label {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* ===== Distance Selector ===== */
.distance-selector {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.preset-distances {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-sm);
}

.distance-btn {
    padding: var(--spacing-sm) var(--spacing-md);
    background: var(--bg-glass);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-full);
    color: var(--text-primary);
    font-size: 0.875rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.distance-btn:hover {
    background: rgba(255, 255, 255, 0.1);
    border-color: rgba(102, 126, 234, 0.3);
}

.distance-btn.active {
    background: var(--primary-gradient);
    border-color: transparent;
    box-shadow: 0 4px 15px rgba(102, 126, 234, 0.4);
}

.custom-distance {
    display: flex;
    gap: var(--spacing-md);
}

.custom-distance input {
    flex: 1;
}

/* ===== Time Inputs ===== */
.time-inputs,
.pace-inputs {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    flex-wrap: wrap;
}

.time-field,
.pace-field {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-xs);
}

.time-field input,
.pace-field input {
    width: 80px;
    text-align: center;
}

.time-label,
.pace-label {
    font-size: 0.75rem;
    color: var(--text-muted);
}

.time-separator,
.pace-separator {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--text-muted);
    margin-top: -20px;
}

/* ===== Form Elements ===== */
input[type="number"],
select {
    padding: var(--spacing-md);
    background: rgba(255, 255, 255, 0.05);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    color: var(--text-primary);
    font-size: 1rem;
    font-family: inherit;
    transition: all var(--transition-fast);
    appearance: none;
    -moz-appearance: textfield;
}

input[type="number"]::-webkit-outer-spin-button,
input[type="number"]::-webkit-inner-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

input[type="number"]:focus,
select:focus {
    outline: none;
    border-color: var(--border-glow);
    box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.2);
}

input[type="number"]::placeholder {
    color: var(--text-muted);
}

select {
    cursor: pointer;
    min-width: 100px;
}

option {
    background-color: var(--bg-secondary);
    color: var(--text-primary);
}

.pace-unit-select {
    margin-left: 0;
}

/* ===== Calculate Button ===== */
.calculate-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-lg) var(--spacing-xl);
    background: var(--primary-gradient);
    border: none;
    border-radius: var(--radius-lg);
    color: var(--text-primary);
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-normal);
    box-shadow: 0 4px 20px rgba(102, 126, 234, 0.4);
}

.calculate-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 30px rgba(102, 126, 234, 0.5);
}

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

.btn-icon {
    width: 20px;
    height: 20px;
    transition: transform var(--transition-fast);
}

.calculate-btn:hover .btn-icon {
    transform: translateX(4px);
}

/* ===== Results Section ===== */
.results-section {
    animation: fadeInUp 0.5s ease;
}

.results-section.hidden {
    display: none;
}

.results-title {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--spacing-lg);
    color: var(--text-primary);
    text-align: center;
}

.results-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-md);
}

.result-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    text-align: center;
    backdrop-filter: blur(20px);
    transition: all var(--transition-normal);
}

.result-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-glow);
    border-color: rgba(102, 126, 234, 0.3);
}

.result-card.primary {
    background: linear-gradient(135deg, rgba(102, 126, 234, 0.15) 0%, rgba(118, 75, 162, 0.15) 100%);
    border-color: rgba(102, 126, 234, 0.3);
}

.result-label {
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.1em;
    margin-bottom: var(--spacing-sm);
}

.result-value {
    font-size: 1.75rem;
    font-weight: 700;
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.result-unit {
    font-size: 0.875rem;
    color: var(--text-secondary);
    margin-top: var(--spacing-xs);
}

/* ===== Pace Chart Section ===== */
.pace-chart-section {
    animation: fadeInUp 0.5s ease 0.1s both;
}

.pace-chart-section.hidden {
    display: none;
}

.chart-title {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
    text-align: center;
}

.pace-chart {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    backdrop-filter: blur(20px);
    max-height: 300px;
    overflow-y: auto;
}

.split-row {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-sm) 0;
    border-bottom: 1px solid var(--border-color);
}

.split-row:last-child {
    border-bottom: none;
}

.split-distance {
    font-weight: 500;
    color: var(--text-primary);
}

.split-time {
    font-family: 'SF Mono', 'Monaco', 'Inconsolata', monospace;
    color: var(--text-secondary);
}

/* ===== Footer ===== */
.footer {
    text-align: center;
    padding: var(--spacing-xl) 0;
    color: var(--text-muted);
    font-size: 0.875rem;
}

/* ===== Animations ===== */
@keyframes fadeIn {
    from {
        opacity: 0;
    }

    to {
        opacity: 1;
    }
}

@keyframes fadeInDown {
    from {
        opacity: 0;
        transform: translateY(-20px);
    }

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

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }

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

/* ===== Responsive Design ===== */
@media (max-width: 600px) {
    .app-container {
        padding: var(--spacing-md);
    }

    .header h1 {
        font-size: 1.75rem;
    }

    .mode-buttons {
        grid-template-columns: 1fr;
    }

    .mode-btn {
        flex-direction: row;
        justify-content: flex-start;
        gap: var(--spacing-md);
        padding: var(--spacing-md);
    }

    .mode-desc {
        margin-left: auto;
    }

    .preset-distances {
        justify-content: center;
    }

    .time-inputs,
    .pace-inputs {
        justify-content: center;
    }

    .time-field input,
    .pace-field input {
        width: 60px;
    }

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

    .result-value {
        font-size: 1.5rem;
    }
}

/* ===== Custom Scrollbar ===== */
::-webkit-scrollbar {
    width: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-secondary);
    border-radius: var(--radius-full);
}

::-webkit-scrollbar-thumb {
    background: rgba(255, 255, 255, 0.2);
    border-radius: var(--radius-full);
}

::-webkit-scrollbar-thumb:hover {
    background: rgba(255, 255, 255, 0.3);
}