:root {
    --bg-primary: #f5f7fa;
    --bg-secondary: #ffffff;
    --text-primary: #1a1a2e;
    --text-secondary: #4a4a6a;
    --accent: #10b981;
    --accent-hover: #059669;
    --border: #e0e6ed;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    --radius: 12px;
}

[data-theme="dark"] {
    --bg-primary: #0f0f1a;
    --bg-secondary: #1a1a2e;
    --text-primary: #ffffff;
    --text-secondary: #a0a0c0;
    --border: #2d2d4a;
}

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

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

.container { max-width: 900px; margin: 0 auto; padding: 20px; }

header {
    text-align: center;
    padding: 40px 20px;
    background: var(--bg-secondary);
    border-radius: var(--radius);
    margin-bottom: 30px;
    box-shadow: var(--shadow);
    position: relative;
}

header h1 { font-size: 2.5rem; margin-bottom: 10px; color: var(--accent); }
.tagline { color: var(--text-secondary); }

.dark-mode-btn {
    position: absolute;
    top: 20px;
    right: 20px;
    background: var(--bg-primary);
    border: 2px solid var(--border);
    border-radius: 50%;
    width: 45px;
    height: 45px;
    font-size: 1.3rem;
    cursor: pointer;
}

.calculator-card {
    background: var(--bg-secondary);
    border-radius: var(--radius);
    padding: 30px;
    margin-bottom: 25px;
    box-shadow: var(--shadow);
}

.calculator-card h2 {
    color: var(--accent);
    margin-bottom: 20px;
    font-size: 1.3rem;
    border-bottom: 2px solid var(--border);
    padding-bottom: 10px;
}

.calc-form { display: flex; flex-direction: column; gap: 15px; }

.input-group { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.input-group.vertical { flex-direction: column; align-items: stretch; }
.input-row { display: flex; align-items: center; gap: 15px; }
.input-row label { min-width: 120px; font-weight: 500; }

.input-group input {
    flex: 1;
    min-width: 100px;
    max-width: 150px;
    padding: 12px 15px;
    border: 2px solid var(--border);
    border-radius: 8px;
    font-size: 1.1rem;
    background: var(--bg-primary);
    color: var(--text-primary);
}

.input-group input:focus { outline: none; border-color: var(--accent); }

.calc-btn {
    background: var(--accent);
    color: white;
    border: none;
    padding: 14px 30px;
    border-radius: 8px;
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    align-self: flex-start;
}

.calc-btn:hover { background: var(--accent-hover); transform: translateY(-2px); }

.result {
    padding: 20px;
    background: rgba(16, 185, 129, 0.1);
    border-radius: 8px;
    font-size: 1.4rem;
    font-weight: 700;
    color: var(--accent);
    min-height: 65px;
    border-left: 4px solid var(--accent);
}

.result.error { border-left-color: #e74c3c; color: #e74c3c; font-size: 1rem; }

.trust-badges {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 15px;
    margin: 40px 0;
}

.badge {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 15px 20px;
    background: var(--bg-secondary);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    font-weight: 600;
    color: var(--text-secondary);
}

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

.faq-section {
    background: var(--bg-secondary);
    border-radius: var(--radius);
    padding: 30px;
    margin: 30px 0;
    box-shadow: var(--shadow);
}

.faq-section h2 { color: var(--accent); margin-bottom: 20px; }

.faq-item { border-bottom: 1px solid var(--border); padding: 15px 0; }
.faq-item:last-child { border-bottom: none; }

.faq-item summary {
    font-weight: 600;
    cursor: pointer;
    padding: 10px 0;
    list-style: none;
}

.faq-item summary::after { content: '+'; float: right; font-size: 1.5rem; color: var(--accent); }
.faq-item[open] summary::after { content: '−'; }
.faq-item p { padding: 15px 0; color: var(--text-secondary); }

footer { text-align: center; padding: 30px; color: var(--text-secondary); }

@media (max-width: 768px) {
    header h1 { font-size: 1.8rem; }
    .dark-mode-btn { position: static; margin-top: 15px; }
    .input-group { flex-direction: column; align-items: stretch; }
    .input-group input { max-width: 100%; }
    .input-row { flex-direction: column; gap: 5px; }
    .input-row label { min-width: auto; }
    .calc-btn { width: 100%; }
}