@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&display=swap');

:root {
    --primary-color: #4a6bff;
    --primary-hover: #3a5bef;
    --secondary-color: #ff6b6b;
    --accent-color: #6bff6b;
    --background-color: #f5f7fa;
    --card-background: #ffffff;
    --text-color: #333;
    --text-secondary: #7f8c8d;
    --border-color: #ddd;
    --shadow-color: rgba(0, 0, 0, 0.1);
    --input-background: #ffffff;
    --gradient-primary: linear-gradient(135deg, #4a6bff 0%, #3a5bef 100%);
    --gradient-secondary: linear-gradient(135deg, #ff6b6b 0%, #ff5252 100%);
    --gradient-accent: linear-gradient(135deg, #6bff6b 0%, #52ff52 100%);
    --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
}

[data-theme="dark"] {
    --primary-color: #4a6bff;
    --primary-hover: #3a5bef;
    --secondary-color: #ff6b6b;
    --accent-color: #6bff6b;
    --background-color: #1a1a1a;
    --card-background: #2d2d2d;
    --text-color: #ffffff;
    --text-secondary: #b0b0b0;
    --border-color: #404040;
    --shadow-color: rgba(0, 0, 0, 0.3);
    --input-background: #404040;
    --gradient-primary: linear-gradient(135deg, #4a6bff 0%, #3a5bef 100%);
    --gradient-secondary: linear-gradient(135deg, #ff6b6b 0%, #ff5252 100%);
    --gradient-accent: linear-gradient(135deg, #6bff6b 0%, #52ff52 100%);
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(20px); }
    to { opacity: 1; transform: translateY(0); }
}

@keyframes pulse {
    0% { transform: scale(1); }
    50% { transform: scale(1.05); }
    100% { transform: scale(1); }
}

@keyframes slideIn {
    from { transform: translateX(-100px); opacity: 0; }
    to { transform: translateX(0); opacity: 1; }
}

@keyframes glow {
    0% { box-shadow: 0 0 5px var(--primary-color); }
    50% { box-shadow: 0 0 20px var(--primary-color); }
    100% { box-shadow: 0 0 5px var(--primary-color); }
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    transition: background-color 0.3s, color 0.3s, border-color 0.3s, transform 0.3s;
}

body {
    font-family: var(--font-primary);
    line-height: 1.6;
    background-color: var(--background-color);
    color: var(--text-color);
    animation: fadeIn 0.5s ease-out;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
    width: 100%;
    flex: 1;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 3rem;
    padding: 1.5rem;
    background: var(--gradient-primary);
    border-radius: 15px;
    box-shadow: 0 4px 15px var(--shadow-color);
    animation: slideIn 0.5s ease-out;
    text-align: center;
}

.header-content {
    flex: 1;
    max-width: 800px;
    margin: 0 auto;
}

header h1 {
    color: white;
    margin-bottom: 0.5rem;
    font-size: 2.5rem;
    font-weight: 700;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
    letter-spacing: -0.02em;
}

header p {
    color: rgba(255, 255, 255, 0.9);
    font-size: 1.1rem;
    max-width: 600px;
    margin: 0 auto;
    font-weight: 400;
    letter-spacing: -0.01em;
}

.theme-toggle {
    background: rgba(255, 255, 255, 0.2);
    border: none;
    color: white;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.8rem 1.5rem;
    border-radius: 25px;
    font-size: 1rem;
    transition: all 0.3s ease;
    backdrop-filter: blur(5px);
    position: absolute;
    top: 1rem;
    right: 1rem;
}

.theme-toggle:hover {
    background: rgba(255, 255, 255, 0.3);
    transform: translateY(-2px);
}

.calculator {
    background: var(--card-background);
    border-radius: 20px;
    box-shadow: 0 8px 20px var(--shadow-color);
    padding: 2.5rem;
    display: flex;
    flex-direction: column;
    gap: 2.5rem;
    animation: fadeIn 0.7s ease-out;
    max-width: 1000px;
    margin: 0 auto;
}

.input-section {
    display: flex;
    flex-direction: column;
    gap: 1.8rem;
    max-width: 500px;
    margin: 0 auto;
    width: 100%;
}

.input-group {
    display: flex;
    flex-direction: column;
    gap: 0.8rem;
    animation: fadeIn 0.5s ease-out;
}

label {
    font-weight: 500;
    color: var(--text-color);
    font-size: 1.1rem;
    transition: color 0.3s ease;
    letter-spacing: -0.01em;
}

input {
    padding: 1.2rem;
    border: 2px solid var(--border-color);
    border-radius: 12px;
    font-size: 1.1rem;
    background-color: var(--input-background);
    color: var(--text-color);
    transition: all 0.3s ease;
    width: 100%;
    font-family: var(--font-primary);
    letter-spacing: -0.01em;
}

input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(74, 107, 255, 0.2);
    transform: translateY(-2px);
}

.primary-button {
    background: var(--gradient-primary);
    color: white;
    border: none;
    padding: 1.2rem 2.5rem;
    border-radius: 12px;
    font-size: 1.1rem;
    cursor: pointer;
    transition: all 0.3s ease;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    position: relative;
    overflow: hidden;
    width: 100%;
    max-width: 300px;
    margin: 0 auto;
    font-family: var(--font-primary);
}

.primary-button:hover {
    transform: translateY(-3px);
    box-shadow: 0 8px 15px rgba(74, 107, 255, 0.3);
    animation: pulse 1s infinite;
}

.primary-button:active {
    transform: translateY(-1px);
}

.results-section {
    display: flex;
    flex-direction: column;
    gap: 2.5rem;
    max-width: 800px;
    margin: 0 auto;
    width: 100%;
}

.result-card, .strategy-card {
    background: var(--card-background);
    border-radius: 15px;
    padding: 2rem;
    box-shadow: 0 4px 15px var(--shadow-color);
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
    text-align: center;
}

.result-card:hover, .strategy-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 20px var(--shadow-color);
}

.result-card h3, .strategies-section h3 {
    color: var(--text-color);
    margin-bottom: 1.2rem;
    font-size: 1.4rem;
    font-weight: 600;
    background: var(--gradient-primary);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    text-align: center;
    letter-spacing: -0.02em;
}

.strategy-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1.5rem;
}

.strategy-card {
    text-align: center;
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
}

.strategy-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 5px;
    background: var(--gradient-primary);
    transform: scaleX(0);
    transform-origin: left;
    transition: transform 0.3s ease;
}

.strategy-card:hover::before {
    transform: scaleX(1);
}

.strategy-card h4 {
    color: var(--text-color);
    margin-bottom: 0.8rem;
    font-size: 1.3rem;
    font-weight: 600;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    letter-spacing: -0.02em;
}

.strategy-card p {
    color: var(--text-secondary);
    font-size: 1rem;
    margin-bottom: 1.2rem;
}

#snowball-results, #avalanche-results {
    animation: fadeIn 0.5s ease-out;
}

.strategy-tips {
    margin-top: 1.5rem;
    padding-top: 1rem;
    border-top: 1px solid var(--border-color);
}

.strategy-tips h5 {
    color: var(--text-color);
    margin-bottom: 0.8rem;
    font-size: 1.1rem;
}

.strategy-tips ul {
    list-style: none;
    padding: 0;
}

.strategy-tips li {
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
    padding-left: 1.5rem;
    position: relative;
}

.strategy-tips li::before {
    content: '✓';
    color: var(--accent-color);
    position: absolute;
    left: 0;
}

.tips-section, .additional-methods {
    max-width: 800px;
    margin: 0 auto;
    width: 100%;
}

.tips-grid, .method-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
}

.tip-card, .method-card {
    background: var(--card-background);
    border-radius: 15px;
    padding: 1.5rem;
    box-shadow: 0 4px 15px var(--shadow-color);
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
    text-align: center;
}

.tip-card:hover, .method-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 20px var(--shadow-color);
}

.tip-card i {
    font-size: 2.5rem;
    color: var(--primary-color);
    margin-bottom: 1rem;
}

.tip-card h4 {
    color: var(--text-color);
    margin-bottom: 1rem;
    font-size: 1.2rem;
    font-weight: 600;
    letter-spacing: -0.02em;
}

.tip-card p {
    color: var(--text-secondary);
    font-size: 0.95rem;
    line-height: 1.5;
}

.method-card {
    background: var(--card-background);
    border-radius: 15px;
    padding: 1.5rem;
    box-shadow: 0 4px 15px var(--shadow-color);
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
}

.method-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 20px var(--shadow-color);
}

.method-card h4 {
    color: var(--text-color);
    margin-bottom: 1rem;
    font-size: 1.2rem;
    font-weight: 600;
    letter-spacing: -0.02em;
}

.method-card h4 i {
    color: var(--primary-color);
}

.method-card p {
    color: var(--text-secondary);
    margin-bottom: 1rem;
    line-height: 1.5;
}

.method-card ul {
    list-style: none;
    padding: 0;
}

.method-card li {
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
    padding-left: 1.5rem;
    position: relative;
}

.method-card li::before {
    content: '•';
    color: var(--accent-color);
    position: absolute;
    left: 0;
    font-size: 1.2rem;
}

@media (max-width: 768px) {
    .container {
        padding: 1rem;
    }

    header {
        flex-direction: column;
        text-align: center;
        gap: 1.5rem;
        padding: 1.5rem;
        position: relative;
    }

    .theme-toggle {
        position: static;
        margin-top: 1rem;
    }

    .calculator {
        padding: 1.5rem;
    }

    .strategy-cards, .tips-grid, .method-cards {
        grid-template-columns: 1fr;
    }

    .primary-button {
        width: 100%;
        max-width: none;
    }

    .input-section {
        max-width: none;
    }

    .result-card, .strategy-card, .tip-card, .method-card {
        padding: 1.5rem;
    }

    header h1 {
        font-size: 2rem;
        letter-spacing: -0.03em;
    }

    header p {
        font-size: 1rem;
        letter-spacing: -0.01em;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0.5rem;
    }

    header {
        padding: 1rem;
    }

    .calculator {
        padding: 1rem;
    }

    input {
        padding: 1rem;
        font-size: 1rem;
    }

    .primary-button {
        padding: 1rem;
        font-size: 1rem;
    }
}

.payment-comparison {
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px solid var(--border-color);
    font-size: 0.9rem;
    text-align: left;
}

.payment-comparison .increase {
    color: var(--accent-color);
    display: block;
    margin-bottom: 0.5rem;
}

.payment-comparison .decrease {
    color: var(--secondary-color);
    display: block;
}

#snowball-results p,
#avalanche-results p {
    margin-bottom: 0.8rem;
    line-height: 1.5;
}

#snowball-results span,
#avalanche-results span {
    font-weight: 600;
    color: var(--primary-color);
}