:root {
    --primary-color: #1870C8;
    --secondary-color: #F5F7FA;
    --text-color: #333;
    --light-text: #666;
    --white: #ffffff;
    --container-width: 1100px;
}

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

body {
    font-family: 'Nanum Gothic', sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--white);
    overflow-x: hidden;
}

.container {
    max-width: var(--container-width);
    margin: 0 auto;
    padding: 0 20px;
}

.text-center {
    text-align: center;
}

/* Header & Nav */
header {
    background: var(--white);
    box-shadow: 0 2px 10px rgba(0,0,0,0.05);
    position: sticky;
    top: 0;
    z-index: 1000;
    padding: 15px 0;
}

nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    display: flex;
    align-items: center;
    gap: 10px;
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--primary-color);
}

.logo img {
    height: 40px;
    width: 40px;
}

.nav-links {
    display: flex;
    align-items: center;
    gap: 20px;
}

.nav-links a {
    text-decoration: none;
    color: var(--text-color);
    font-weight: 700;
    transition: color 0.3s;
}

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

/* Buttons */
.btn {
    display: inline-block;
    padding: 12px 30px;
    border-radius: 8px;
    text-decoration: none;
    font-weight: 700;
    transition: all 0.3s;
    cursor: pointer;
}

.btn-small {
    padding: 8px 15px;
    background: var(--primary-color);
    color: var(--white) !important;
    border-radius: 6px;
}

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

.btn-primary:hover {
    background: #145da0;
    transform: translateY(-2px);
}

.btn-outline {
    border: 2px solid var(--primary-color);
    color: var(--primary-color);
}

.btn-outline:hover {
    background: var(--primary-color);
    color: var(--white);
}

/* Hamburger Button */
.hamburger {
    display: none;
    flex-direction: column;
    justify-content: center;
    gap: 5px;
    cursor: pointer;
    background: none;
    border: none;
    padding: 6px;
    border-radius: 6px;
    transition: background 0.2s;
}

.hamburger:hover {
    background: var(--secondary-color);
}

.hamburger span {
    display: block;
    width: 22px;
    height: 2px;
    background: var(--text-color);
    border-radius: 2px;
    transition: transform 0.3s, opacity 0.3s;
}

.hamburger.open span:nth-child(1) {
    transform: rotate(45deg) translate(5px, 5px);
}

.hamburger.open span:nth-child(2) {
    opacity: 0;
    transform: translateX(-8px);
}

.hamburger.open span:nth-child(3) {
    transform: rotate(-45deg) translate(5px, -5px);
}

/* Hero Section */
.hero {
    padding: 80px 0;
    background: linear-gradient(135deg, #f0f4f8 0%, #ffffff 100%);
}

.hero-grid {
    display: grid;
    grid-template-columns: 1.2fr 0.8fr;
    align-items: center;
    gap: 40px;
}

.hero-text h1 {
    font-size: 3rem;
    line-height: 1.2;
    margin-bottom: 20px;
    color: #1a202c;
}

.hero-text h1 span {
    color: var(--primary-color);
}

.hero-text p {
    font-size: 1.1rem;
    color: var(--light-text);
    margin-bottom: 30px;
}

.cta-buttons {
    display: flex;
    gap: 15px;
}

.app-screenshot {
    width: 100%;
    max-width: 350px;
    border-radius: 30px;
    box-shadow: 0 20px 40px rgba(0,0,0,0.1);
    display: block;
    margin: 0 auto;
}

/* Screenshot Showcase */
.screenshot-showcase {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 20px;
    width: 100%;
}

.phone-mockup {
    position: relative;
    width: 100%;
    max-width: 320px;
    border-radius: 36px;
    padding: 10px;
    background: #0f172a;
    box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.25), 0 0 0 6px #1e293b;
    overflow: hidden;
    transition: transform 0.3s ease;
}

.phone-mockup:hover {
    transform: translateY(-5px);
}

.phone-screen {
    position: relative;
    width: 100%;
    aspect-ratio: 9 / 19.5;
    border-radius: 28px;
    overflow: hidden;
    background: #000;
}

.phone-screen img {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    object-fit: cover;
    opacity: 0;
    transition: opacity 0.5s ease;
}

.phone-screen img.active {
    opacity: 1;
}

.showcase-tabs {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 8px;
    width: 100%;
    max-width: 500px;
}

.tab-btn {
    padding: 8px 16px;
    font-size: 0.85rem;
    font-weight: 700;
    color: var(--light-text);
    background: var(--white);
    border: 1px solid #e2e8f0;
    border-radius: 20px;
    cursor: pointer;
    transition: all 0.3s;
}

.tab-btn:hover {
    color: var(--primary-color);
    border-color: var(--primary-color);
    background: #f0f7ff;
}

.tab-btn.active {
    color: var(--white);
    background: var(--primary-color);
    border-color: var(--primary-color);
    box-shadow: 0 4px 12px rgba(24, 112, 200, 0.2);
}

/* Features Section */
.features {
    padding: 100px 0;
}

.section-title {
    text-align: center;
    font-size: 2.2rem;
    margin-bottom: 60px;
}

.feature-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 30px;
}

.feature-card {
    padding: 40px;
    background: var(--secondary-color);
    border-radius: 16px;
    text-align: center;
    transition: transform 0.3s;
}

.feature-card:hover {
    transform: translateY(-10px);
}

.feature-card .icon {
    font-size: 3rem;
    margin-bottom: 20px;
}

.feature-card h3 {
    margin-bottom: 15px;
    color: var(--primary-color);
}

/* How to Section */
.how-to {
    padding: 100px 0;
    background: #f8fafc;
}

.steps-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 40px;
}

.step {
    text-align: center;
    position: relative;
}

.step-num {
    width: 50px;
    height: 50px;
    background: var(--primary-color);
    color: var(--white);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 800;
    font-size: 1.5rem;
    margin: 0 auto 20px;
}

.step h4 {
    font-size: 1.3rem;
    margin-bottom: 15px;
}

/* Download Section */
.download {
    padding: 100px 0;
    background: var(--primary-color);
    color: var(--white);
}

.download h2 {
    font-size: 2.5rem;
    margin-bottom: 20px;
}

.download p {
    font-size: 1.2rem;
    margin-bottom: 40px;
    opacity: 0.9;
}

.store-buttons {
    display: flex;
    justify-content: center;
    gap: 20px;
    flex-wrap: wrap;
}

.store-btn {
    background: #000;
    color: white;
    padding: 15px 30px;
    border-radius: 10px;
    text-decoration: none;
    font-weight: 700;
    min-width: 200px;
    text-align: center;
}

/* Footer */
footer {
    padding: 60px 0;
    background: #1a202c;
    color: #a0aec0;
}

.footer-content {
    display: flex;
    justify-content: space-between;
    flex-wrap: wrap;
    gap: 40px;
}

.footer-info h4 {
    color: var(--white);
    margin-bottom: 20px;
    font-size: 1.5rem;
}

.disclaimer {
    font-size: 0.85rem;
    margin-top: 15px;
    color: #718096;
}

.footer-contact {
    text-align: right;
}

.footer-link {
    color: var(--white);
    text-decoration: none;
    background: rgba(255, 255, 255, 0.1);
    padding: 8px 15px;
    border-radius: 6px;
    transition: background 0.3s;
    display: inline-block;
    margin-bottom: 10px;
}

.footer-link:hover {
    background: rgba(255, 255, 255, 0.2);
}

/* Responsive */
@media (max-width: 768px) {
    .hero-grid {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .hero-text h1 {
        font-size: 2.2rem;
    }

    .cta-buttons {
        justify-content: center;
    }

    .hamburger {
        display: flex;
    }

    .nav-links {
        display: none;
        position: absolute;
        top: 72px;
        left: 0;
        right: 0;
        flex-direction: column;
        align-items: flex-start;
        background: var(--white);
        padding: 20px 24px;
        box-shadow: 0 6px 16px rgba(0, 0, 0, 0.08);
        gap: 16px;
        z-index: 999;
    }

    .nav-links.open {
        display: flex;
    }

    .footer-content {
        flex-direction: column;
        text-align: center;
    }

    .footer-contact {
        text-align: center;
    }
}

/* FAQ Section */
.faq {
    padding: 100px 0;
    background: var(--white);
}

.faq-list {
    max-width: 800px;
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    gap: 15px;
}

.faq-item {
    border: 1px solid #e2e8f0;
    border-radius: 12px;
    background: #f8fafc;
    overflow: hidden;
    transition: all 0.3s ease;
}

.faq-item.open {
    border-color: var(--primary-color);
    box-shadow: 0 4px 20px rgba(24, 112, 200, 0.05);
    background: var(--white);
}

.faq-question {
    width: 100%;
    padding: 20px 24px;
    background: none;
    border: none;
    text-align: left;
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--text-color);
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 15px;
    outline: none;
}

.faq-question:hover {
    color: var(--primary-color);
}

.faq-question .icon-arrow {
    display: inline-block;
    width: 10px;
    height: 10px;
    border-right: 2px solid #a0aec0;
    border-bottom: 2px solid #a0aec0;
    transform: rotate(45deg);
    transition: transform 0.3s ease, border-color 0.3s ease;
    flex-shrink: 0;
    margin-bottom: 4px;
}

.faq-item.open .faq-question .icon-arrow {
    transform: rotate(-135deg);
    border-color: var(--primary-color);
    margin-bottom: -2px;
}

.faq-answer {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.3s ease, padding 0.3s ease;
    padding: 0 24px;
    font-size: 0.95rem;
    color: var(--light-text);
    line-height: 1.7;
    border-top: 1px solid transparent;
}

.faq-item.open .faq-answer {
    max-height: 300px;
    padding: 20px 24px;
    border-color: #f1f5f9;
}

.faq-answer strong {
    color: var(--primary-color);
}

/* Web Calculator Section */
.web-calc {
    padding: 100px 0;
    background: var(--white);
}

.calc-container {
    max-width: 900px;
    margin: 0 auto;
    background: var(--white);
    border-radius: 24px;
    box-shadow: 0 20px 50px rgba(0,0,0,0.1);
    padding: 40px;
    border: 1px solid #eef2f7;
}

.calc-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 40px;
    align-items: center;
}

@media (max-width: 768px) {
    .calc-grid {
        grid-template-columns: 1fr;
    }
    .calc-container {
        padding: 24px;
    }
}

.calc-inputs {
    display: flex;
    flex-direction: column;
    gap: 24px;
}

.input-group {
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.input-group label {
    font-weight: 700;
    font-size: 0.95rem;
    color: var(--text-color);
    display: flex;
    justify-content: space-between;
}

.input-group label span {
    color: var(--primary-color);
    font-size: 1.1rem;
}

.input-group select, .input-group input[type="range"] {
    width: 100%;
}

select {
    padding: 12px;
    border-radius: 8px;
    border: 2px solid #e2e8f0;
    font-family: inherit;
    font-size: 1rem;
    outline: none;
    transition: border-color 0.3s;
}

select:focus {
    border-color: var(--primary-color);
}

input[type="range"] {
    -webkit-appearance: none;
    height: 8px;
    background: #e2e8f0;
    border-radius: 5px;
    outline: none;
}

input[type="range"]::-webkit-slider-thumb {
    -webkit-appearance: none;
    width: 24px;
    height: 24px;
    background: var(--primary-color);
    border-radius: 50%;
    cursor: pointer;
    box-shadow: 0 0 10px rgba(24, 112, 200, 0.3);
}

.toggle-group {
    display: flex;
    align-items: center;
    gap: 15px;
    background: #f8fafc;
    padding: 12px 20px;
    border-radius: 12px;
    cursor: pointer;
}

.toggle-group input {
    width: 20px;
    height: 20px;
    cursor: pointer;
}

.calc-result {
    text-align: center;
    padding: 30px;
    background: #f8fafc;
    border-radius: 20px;
    display: flex;
    flex-direction: column;
    gap: 15px;
    min-height: 280px;
    justify-content: center;
}

.result-temp {
    font-size: 4rem;
    font-weight: 800;
    color: var(--text-color);
    line-height: 1;
}

.result-label {
    display: inline-block;
    padding: 8px 20px;
    border-radius: 50px;
    font-weight: 800;
    font-size: 1.2rem;
    color: var(--white);
    background: #cbd5e1;
    transition: all 0.3s;
}

.result-rest {
    font-weight: 700;
    color: var(--light-text);
    font-size: 1.1rem;
}

.calc-footer {
    margin-top: 30px;
    text-align: center;
    font-size: 0.9rem;
    color: var(--light-text);
}

.calc-footer a {
    color: var(--primary-color);
    font-weight: 700;
    text-decoration: none;
}