:root {
    --bg: #0d0f14;
    --bg-alt: #141821;
    --text: #e8eaf0;
    --muted: #9aa3b2;
    --accent: #6c5ce7;
    --accent-2: #00d1ff;
    --radius: 14px;
    --border: rgba(255, 255, 255, 0.08);
}

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

body {
    font-family: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.container {
    width: 100%;
    max-width: 900px;
    margin: 0 auto;
    padding: 0 24px;
}

/* Header */
.header {
    position: sticky;
    top: 0;
    z-index: 100;
    background: rgba(13, 15, 20, 0.85);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border-bottom: 1px solid rgba(255, 255, 255, 0.06);
}

.header__inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 64px;
}

.logo {
    font-weight: 800;
    font-size: 20px;
    letter-spacing: -0.3px;
}
.logo span {
    background: linear-gradient(90deg, var(--accent), var(--accent-2));
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
}

/* Main */
.main { flex: 1; padding-bottom: 64px; }

.hero {
    text-align: center;
    padding: 56px 0 32px;
}
.hero h1 {
    font-size: clamp(28px, 5vw, 42px);
    font-weight: 800;
    letter-spacing: -0.8px;
}
.subtitle {
    color: var(--muted);
    max-width: 560px;
    margin: 12px auto 0;
    font-size: clamp(15px, 2.4vw, 17px);
}

/* Tabs */
.tabs {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    justify-content: center;
    margin-bottom: 28px;
}
.tab {
    appearance: none;
    border: 1px solid var(--border);
    background: var(--bg-alt);
    color: var(--muted);
    font: inherit;
    font-weight: 600;
    font-size: 14px;
    padding: 9px 18px;
    border-radius: 999px;
    cursor: pointer;
    transition: color 0.15s, border-color 0.15s, background 0.15s, transform 0.1s;
}
.tab:hover { color: var(--text); border-color: rgba(255, 255, 255, 0.18); }
.tab:active { transform: scale(0.97); }
.tab--active {
    background: linear-gradient(135deg, var(--accent), var(--accent-2));
    border-color: transparent;
    color: #fff;
}

/* Converter card */
.converter {
    background: var(--bg-alt);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 28px;
    box-shadow: 0 12px 40px rgba(0, 0, 0, 0.35);
}

.converter__row {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    gap: 16px;
    align-items: end;
}

.field { display: flex; flex-direction: column; gap: 8px; min-width: 0; }
.field__label {
    font-size: 12px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.8px;
    color: var(--muted);
}
.field__input {
    appearance: none;
    width: 100%;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: 10px;
    color: var(--text);
    font: inherit;
    font-size: 20px;
    font-weight: 600;
    padding: 13px 16px;
    transition: border-color 0.15s, box-shadow 0.15s;
}
.field__input::placeholder { color: rgba(154, 163, 178, 0.5); font-weight: 400; }
.field__input:focus {
    outline: none;
    border-color: var(--accent-2);
    box-shadow: 0 0 0 3px rgba(0, 209, 255, 0.15);
}
.field__input--invalid {
    border-color: #e5484d;
}
.field__input--invalid:focus { box-shadow: 0 0 0 3px rgba(229, 72, 77, 0.15); }
.field__select {
    appearance: none;
    width: 100%;
    background: var(--bg) url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='8' viewBox='0 0 12 8'%3E%3Cpath d='M1 1l5 5 5-5' stroke='%239aa3b2' stroke-width='2' fill='none' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E") no-repeat right 14px center;
    border: 1px solid var(--border);
    border-radius: 10px;
    color: var(--text);
    font: inherit;
    font-size: 15px;
    padding: 11px 38px 11px 14px;
    cursor: pointer;
    transition: border-color 0.15s, box-shadow 0.15s;
}
.field__select:focus {
    outline: none;
    border-color: var(--accent-2);
    box-shadow: 0 0 0 3px rgba(0, 209, 255, 0.15);
}

.swap {
    appearance: none;
    align-self: end;
    margin-bottom: 2px;
    width: 46px;
    height: 46px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: linear-gradient(135deg, var(--accent), var(--accent-2));
    border: none;
    border-radius: 50%;
    color: #fff;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.15s;
}
.swap:hover { transform: rotate(180deg); box-shadow: 0 4px 18px rgba(108, 92, 231, 0.45); }
.swap:active { transform: rotate(180deg) scale(0.92); }

.error {
    color: #e5484d;
    font-size: 14px;
    margin-top: 14px;
}

.formula {
    margin-top: 20px;
    padding-top: 18px;
    border-top: 1px solid var(--border);
    color: var(--muted);
    font-size: 14px;
    text-align: center;
    min-height: 22px;
}
.formula strong { color: var(--text); font-weight: 600; }

/* Reference */
.reference { margin-top: 40px; }
.reference h2 {
    font-size: 20px;
    font-weight: 700;
    margin-bottom: 16px;
}
.reference__grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
    gap: 12px;
}
.reference__item {
    background: var(--bg-alt);
    border: 1px solid var(--border);
    border-radius: 10px;
    padding: 12px 16px;
    font-size: 14px;
    color: var(--muted);
    cursor: pointer;
    transition: border-color 0.15s, color 0.15s, transform 0.1s;
}
.reference__item:hover { border-color: rgba(255, 255, 255, 0.18); color: var(--text); transform: translateY(-1px); }
.reference__item strong { color: var(--accent-2); font-weight: 600; }

/* Footer */
.footer {
    border-top: 1px solid rgba(255, 255, 255, 0.06);
    padding: 20px 0;
    color: var(--muted);
    font-size: 14px;
}
.footer__inner { text-align: center; }

/* Mobile */
@media (max-width: 640px) {
    .hero { padding: 40px 0 24px; }
    .converter { padding: 20px; }
    .converter__row {
        grid-template-columns: 1fr;
        gap: 12px;
    }
    .swap {
        justify-self: center;
        margin: 0;
        transform: rotate(90deg);
    }
    .swap:hover { transform: rotate(270deg); box-shadow: 0 4px 18px rgba(108, 92, 231, 0.45); }
    .swap:active { transform: rotate(270deg) scale(0.92); }
    .field__input { font-size: 18px; }
}