:root {
    --primary-color: #2563EB;
    --primary-hover: #1D4ED8;
    --bg-color: #F8FAFC;
    --card-bg: #FFFFFF;
    --text-main: #0F172A;
    --text-muted: #64748B;
    --border-color: #E2E8F0;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    --shadow-soft: 0 20px 40px rgba(0, 0, 0, 0.05);
    --radius-md: 12px;
    --radius-lg: 18px;
    --success: #10B981;
    --error: #EF4444;
}

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

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
    line-height: 1.5;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

/* Header */
.header {
    background-color: var(--card-bg);
    padding: 1rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    box-shadow: var(--shadow-sm);
    position: sticky;
    top: 0;
    z-index: 100;
}

.logo {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--primary-color);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.nav ul {
    display: flex;
    list-style: none;
    gap: 2rem;
}

.nav a {
    text-decoration: none;
    color: var(--text-muted);
    font-weight: 500;
    transition: color 0.2s ease;
}

.nav a:hover, .nav a.active {
    color: var(--primary-color);
}

.header-contact {
    display: flex;
    gap: 1.5rem;
}

.header-contact a {
    text-decoration: none;
    color: var(--text-muted);
    font-size: 0.9rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    transition: color 0.2s ease;
}

.header-contact a:hover {
    color: var(--primary-color);
}

.mobile-menu-btn {
    display: none;
    font-size: 1.5rem;
    cursor: pointer;
    color: var(--text-main);
}

/* Main Container */
.main-container {
    flex: 1;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 2rem;
}

.app-card {
    background-color: var(--card-bg);
    width: 100%;
    max-width: 600px;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-soft);
    padding: 2.5rem;
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.app-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 25px 50px rgba(0, 0, 0, 0.08);
}

.app-header {
    text-align: center;
    margin-bottom: 2rem;
}

.app-header h1 {
    font-size: 1.8rem;
    font-weight: 700;
    color: var(--text-main);
    margin-bottom: 0.5rem;
}

.app-header p {
    color: var(--text-muted);
}

/* Input Section */
.input-section {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.input-group {
    position: relative;
}

.input-group input {
    width: 100%;
    padding: 1rem 1.25rem;
    font-size: 1.1rem;
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    outline: none;
    font-family: 'Inter', sans-serif;
    color: var(--text-main);
    transition: all 0.3s ease;
    background-color: var(--bg-color);
}

.input-group input:focus {
    border-color: var(--primary-color);
    background-color: var(--card-bg);
    box-shadow: 0 0 0 4px rgba(37, 99, 235, 0.1);
}

.input-group input::placeholder {
    color: #94A3B8;
}

/* Hide arrows in number input */
.input-group input::-webkit-outer-spin-button,
.input-group input::-webkit-inner-spin-button {
    -webkit-appearance: none;
    margin: 0;
}
.input-group input[type=number] {
    -moz-appearance: textfield;
}

.button-group {
    display: flex;
    gap: 1rem;
    flex-wrap: wrap;
}

.btn {
    flex: 1;
    padding: 0.875rem 1.25rem;
    border: none;
    border-radius: var(--radius-md);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    font-family: 'Inter', sans-serif;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    transition: all 0.2s ease;
    white-space: nowrap;
}

.btn-primary {
    background-color: var(--primary-color);
    color: #FFFFFF;
}

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

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

.btn-secondary {
    background-color: #EFF6FF;
    color: var(--primary-color);
}

.btn-secondary:hover {
    background-color: #DBEAFE;
    transform: translateY(-2px);
}

.btn-outline {
    background-color: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-muted);
}

.btn-outline:hover {
    background-color: #F1F5F9;
    color: var(--error);
    border-color: #E2E8F0;
}

/* Result Section */
.result-section {
    margin-top: 2rem;
    padding-top: 2rem;
    border-top: 1px solid var(--border-color);
    animation: fadeIn 0.5s ease;
}

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

.result-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
}

.result-header h2 {
    font-size: 1.25rem;
    font-weight: 600;
}

.icon-btn {
    background: transparent;
    border: none;
    color: var(--text-muted);
    font-size: 1.25rem;
    cursor: pointer;
    transition: all 0.2s ease;
    padding: 0.5rem;
    border-radius: 8px;
}

.icon-btn:hover {
    color: var(--primary-color);
    background-color: #EFF6FF;
    transform: scale(1.1);
}

.result-content {
    background-color: var(--bg-color);
    padding: 1.5rem;
    border-radius: var(--radius-md);
    border: 1px solid var(--border-color);
    font-size: 1.1rem;
}

.result-row {
    display: flex;
    justify-content: space-between;
    margin-bottom: 0.75rem;
}

.result-label {
    color: var(--text-muted);
    font-size: 0.95rem;
}

.result-value {
    font-weight: 600;
    color: var(--text-main);
}

.calculation-steps {
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px dashed var(--border-color);
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
    font-family: monospace;
    font-size: 1.2rem;
}

.calc-step {
    color: var(--text-main);
}

.final-result {
    margin-top: 1.5rem;
    padding: 1rem;
    border-radius: 8px;
    font-weight: 600;
    text-align: center;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    font-size: 1.1rem;
}

.is-armstrong {
    background-color: #D1FAE5;
    color: #065F46;
}

.not-armstrong {
    background-color: #FEE2E2;
    color: #991B1B;
}

/* Footer */
.footer {
    background-color: var(--card-bg);
    padding: 1.5rem 2rem;
    text-align: center;
    border-top: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.footer-links {
    display: flex;
    gap: 1.5rem;
}

.footer-links a {
    text-decoration: none;
    color: var(--text-muted);
    font-size: 0.9rem;
    transition: color 0.2s ease;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.footer-links a:hover {
    color: var(--primary-color);
}

/* Toast */
.toast {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    background-color: var(--text-main);
    color: white;
    padding: 1rem 1.5rem;
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    gap: 0.75rem;
    box-shadow: var(--shadow-lg);
    transform: translateY(100px);
    opacity: 0;
    transition: all 0.3s cubic-bezier(0.68, -0.55, 0.265, 1.55);
    z-index: 1000;
}

.toast.show {
    transform: translateY(0);
    opacity: 1;
}

.toast-icon {
    font-size: 1.25rem;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}