:root {
    --bg: #0d1117;
    --surface: #161b22;
    --surface-2: #1f2530;
    --surface-hover: #232a36;
    --border: #2a323d;
    --border-strong: #3a4452;
    --text: #e6edf3;
    --text-dim: #8b949e;
    --accent: #58a6ff;
    --accent-soft: rgba(88, 166, 255, 0.12);
    --success: #3fb950;
    --warning: #d29922;
    --danger: #f85149;
    --hard: #db8937;
    --easy: #58a6ff;
    --radius: 12px;
    --radius-lg: 16px;
    --transition: 160ms cubic-bezier(0.4, 0, 0.2, 1);
}

* { box-sizing: border-box; }

html, body {
    margin: 0; padding: 0;
    background: var(--bg);
    color: var(--text);
    font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Inter",
                 "Segoe UI", system-ui, "Helvetica Neue", Arial, sans-serif;
    font-size: 16px;
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    overscroll-behavior: none;
    text-rendering: optimizeLegibility;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

input, button, textarea, select {
    font: inherit; color: inherit;
    -webkit-tap-highlight-color: transparent;
}

::selection { background: var(--accent-soft); }

/* ---------- Layout ---------- */
.topbar {
    display: flex; align-items: center; justify-content: space-between;
    padding: 0.85rem 1.25rem;
    border-bottom: 1px solid var(--border);
    background: rgba(13, 17, 23, 0.85);
    backdrop-filter: saturate(180%) blur(12px);
    -webkit-backdrop-filter: saturate(180%) blur(12px);
    position: sticky; top: 0; z-index: 10;
    padding-top: max(0.85rem, env(safe-area-inset-top));
}
.brand {
    font-weight: 600; font-size: 1rem; letter-spacing: -0.01em;
    color: var(--text); text-decoration: none;
    display: inline-flex; align-items: center; gap: 0.4rem;
}
.brand-icon { font-size: 1.15rem; }
.brand:hover { text-decoration: none; }
.topbar nav { display: flex; gap: 1.25rem; }
.nav-link { color: var(--text); font-size: 0.9rem; font-weight: 500; }
.nav-link:hover { text-decoration: none; color: var(--accent); }
.nav-link.dim { color: var(--text-dim); }
.nav-link.dim:hover { color: var(--text); }

.container {
    max-width: 720px;
    margin: 0 auto;
    padding: 1.75rem 1.25rem 4rem;
    padding-bottom: max(4rem, env(safe-area-inset-bottom));
}

/* ---------- Typography ---------- */
.page-header {
    display: flex; align-items: center; justify-content: space-between;
    gap: 1rem; margin-bottom: 1.75rem;
}
.page-title {
    font-size: 1.5rem; font-weight: 600;
    margin: 0 0 1.5rem; letter-spacing: -0.02em;
}
.page-header .page-title { margin: 0; }
.subtitle { font-size: 0.95rem; margin-top: 0.25rem; }
.subtitle-inline { font-size: 0.9em; font-weight: 400; }
.dim { color: var(--text-dim); }
.center { text-align: center; }
.small { font-size: 0.85rem; }
.flag { font-size: 1.15em; vertical-align: -0.05em; }

.badge {
    display: inline-flex; align-items: center;
    padding: 0.3rem 0.7rem;
    background: var(--accent-soft);
    border: 1px solid rgba(88, 166, 255, 0.3);
    color: var(--accent);
    border-radius: 999px;
    font-size: 0.82rem; font-weight: 500;
    white-space: nowrap;
}

/* ---------- Buttons ---------- */
.btn {
    display: inline-flex; align-items: center; justify-content: center; gap: 0.5rem;
    background: var(--surface-2); color: var(--text);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 0.65rem 1.1rem;
    font-size: 0.95rem; font-weight: 500;
    text-decoration: none;
    cursor: pointer;
    transition: background var(--transition), border-color var(--transition),
                transform 80ms ease, color var(--transition);
    user-select: none;
}
.btn:hover { background: var(--surface-hover); border-color: var(--border-strong); text-decoration: none; }
.btn:active { transform: scale(0.97); }
.btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.btn.primary { background: var(--accent); border-color: var(--accent); color: #07111c; font-weight: 600; }
.btn.primary:hover { filter: brightness(1.08); border-color: var(--accent); }
.btn.ghost { background: transparent; border-color: transparent; color: var(--text-dim); }
.btn.ghost:hover { background: var(--surface); color: var(--text); }
.btn.disabled { opacity: 0.4; pointer-events: none; }
.btn.big { padding: 1rem 1.5rem; font-size: 1rem; min-height: 56px; }
.btn.tiny {
    padding: 0; font-size: 1rem;
    width: 28px; height: 28px;
    border-radius: 8px;
    line-height: 1;
}
.btn.danger { color: var(--danger); border-color: rgba(248, 81, 73, 0.3); background: transparent; }
.btn.danger:hover { background: rgba(248, 81, 73, 0.12); border-color: var(--danger); }

.actions { display: flex; gap: 0.6rem; flex-wrap: wrap; margin-top: 1rem; }
.stack { display: flex; flex-direction: column; gap: 0.85rem; }

/* ---------- Login ---------- */
.login-wrap { max-width: 340px; margin: 4rem auto 0; }
.login-wrap h1 { font-size: 1.6rem; font-weight: 600; margin: 0 0 0.25rem; letter-spacing: -0.02em; }
.login-wrap .subtitle { margin: 0 0 1.75rem; }
.login-wrap input {
    background: var(--surface); border: 1px solid var(--border);
    border-radius: var(--radius); padding: 0.85rem 1rem; width: 100%;
    color: var(--text); font-size: 1rem;
    transition: border-color var(--transition), background var(--transition);
}
.login-wrap input:focus {
    outline: none;
    border-color: var(--accent);
    background: var(--surface-2);
}

/* ---------- Home / language cards ---------- */
.lang-grid { display: grid; gap: 0.85rem; grid-template-columns: 1fr; }
@media (min-width: 720px) { .lang-grid { grid-template-columns: repeat(3, 1fr); } }

.lang-card {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 1.25rem;
    transition: border-color var(--transition), transform var(--transition);
    display: flex; flex-direction: column; gap: 1rem;
}
.lang-card:hover { border-color: var(--border-strong); }
.lang-card.has-due { border-color: rgba(88, 166, 255, 0.3); }
.lang-head { display: flex; align-items: center; gap: 0.6rem; }
.lang-head h2 { margin: 0; font-size: 1.1rem; font-weight: 500; letter-spacing: -0.01em; }
.metrics {
    display: grid; grid-template-columns: repeat(4, 1fr); gap: 0.5rem;
}
.metric { display: flex; flex-direction: column; align-items: center; gap: 0.15rem; padding: 0.25rem 0; }
.metric-value { font-size: 1.5rem; font-weight: 600; letter-spacing: -0.02em; line-height: 1.1; }
.metric-value.accent { color: var(--accent); }
.metric-value.dim { color: var(--text-dim); font-weight: 500; }
.metric-label {
    font-size: 0.68rem; color: var(--text-dim);
    text-transform: uppercase; letter-spacing: 0.06em; font-weight: 500;
}
.lang-card .actions { margin-top: auto; }

/* ---------- Forms ---------- */
.form label { display: flex; flex-direction: column; gap: 0.4rem; font-size: 0.9rem; font-weight: 500; }
.label-row { display: inline-flex; align-items: baseline; gap: 0.4rem; }
.form input {
    background: var(--surface); border: 1px solid var(--border);
    border-radius: var(--radius); padding: 0.75rem 0.95rem;
    color: var(--text); font-size: 1rem;
    transition: border-color var(--transition), background var(--transition);
}
.form input:focus {
    outline: none;
    border-color: var(--accent);
    background: var(--surface-2);
}

.search { margin-bottom: 1rem; }
.search input {
    width: 100%;
    background: var(--surface); border: 1px solid var(--border);
    border-radius: var(--radius); padding: 0.7rem 1rem;
    color: var(--text);
    transition: border-color var(--transition);
}
.search input:focus { outline: none; border-color: var(--accent); }

.banner {
    padding: 0.8rem 1rem; border-radius: var(--radius); margin-bottom: 1.25rem;
    border: 1px solid var(--border);
    font-size: 0.92rem;
}
.banner.success { background: rgba(63, 185, 80, 0.08); border-color: rgba(63, 185, 80, 0.35); color: #6ee07e; }
.banner.error { background: rgba(248, 81, 73, 0.08); border-color: rgba(248, 81, 73, 0.35); color: #ff8a82; }
.error { color: var(--danger); font-size: 0.9rem; margin: 0; }

/* ---------- Review ---------- */
.review-progress {
    display: flex; justify-content: space-between; align-items: center;
    padding: 0 0 1.25rem;
    font-size: 0.92rem;
}
.card.review {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 2.25rem 1.5rem 1.5rem;
    min-height: 360px;
    display: flex; flex-direction: column; gap: 1.25rem;
}
.card-front { text-align: center; padding: 1.5rem 0 0.5rem; }
.front-word {
    font-size: 2.1rem; font-weight: 500; margin: 0;
    line-height: 1.2; letter-spacing: -0.02em;
    word-break: break-word;
}
@media (min-width: 480px) { .front-word { font-size: 2.6rem; } }

.tags {
    display: flex; gap: 0.4rem; flex-wrap: wrap; justify-content: center;
    margin-bottom: 0.9rem;
}
.tag {
    background: var(--surface-2); border: 1px solid var(--border);
    border-radius: 999px; padding: 0.18rem 0.65rem;
    font-size: 0.74rem; color: var(--text-dim);
    letter-spacing: 0.01em;
}

.separator { height: 1px; background: var(--border); margin: 0.25rem 0 1rem; }
.card-back { text-align: center; }
.back-text {
    font-size: 1.3rem; margin: 0.5rem 0;
    color: var(--text); font-weight: 500; letter-spacing: -0.01em;
}
.example {
    font-style: italic; color: var(--text-dim);
    margin: 0.6rem 0;
}
.notes { color: var(--text-dim); font-size: 0.92rem; margin: 0.4rem 0 0; }

.card-actions { display: flex; justify-content: center; margin-top: auto; }

.grade-row {
    display: grid; grid-template-columns: repeat(4, 1fr); gap: 0.5rem;
    margin-top: auto;
}
.grade {
    flex-direction: column; gap: 0.2rem;
    padding: 0.95rem 0.4rem; min-height: 68px;
    font-weight: 600;
    border-width: 1.5px;
    background: transparent;
}
.grade .g-label { font-size: 1rem; letter-spacing: -0.01em; }
.grade .kbd { opacity: 0.5; }
.kbd {
    display: inline-block; padding: 0.05rem 0.4rem;
    border-radius: 4px;
    background: rgba(255,255,255,0.06);
    font-size: 0.72rem;
    font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, monospace;
    margin-left: 0.4rem;
    font-weight: 500;
    color: var(--text-dim);
}
.grade.again { color: var(--danger); border-color: rgba(248,81,73,0.35); }
.grade.again:hover { background: rgba(248,81,73,0.1); border-color: var(--danger); }
.grade.hard { color: var(--hard); border-color: rgba(219,137,55,0.35); }
.grade.hard:hover { background: rgba(219,137,55,0.1); border-color: var(--hard); }
.grade.good { color: var(--success); border-color: rgba(63,185,80,0.35); }
.grade.good:hover { background: rgba(63,185,80,0.1); border-color: var(--success); }
.grade.easy { color: var(--easy); border-color: rgba(88,166,255,0.35); }
.grade.easy:hover { background: rgba(88,166,255,0.1); border-color: var(--easy); }

/* ---------- Done ---------- */
.done-wrap { text-align: center; padding: 4rem 1rem 2rem; }
.done-emoji { font-size: 3.5rem; margin-bottom: 0.5rem; }
.done-wrap h2 { font-size: 1.5rem; margin: 0.5rem 0; font-weight: 600; letter-spacing: -0.02em; }
.done-wrap .actions { justify-content: center; }

/* ---------- Cards list ---------- */
.list-count { margin: 0 0 0.75rem; }
.card-list { list-style: none; padding: 0; margin: 0 0 1.5rem; display: flex; flex-direction: column; gap: 0.5rem; }
.card-row {
    display: flex; flex-direction: column; gap: 0.35rem;
    padding: 0.85rem 1rem;
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    transition: border-color var(--transition);
}
.card-row:hover { border-color: var(--border-strong); }
.card-row-main { display: flex; flex-direction: column; gap: 0.2rem; }
.card-row-head { display: flex; gap: 0.5rem; align-items: baseline; flex-wrap: wrap; }
.card-row-head strong { font-weight: 600; letter-spacing: -0.01em; }
.card-row-meta {
    display: flex; align-items: center; gap: 0.6rem; flex-wrap: wrap;
    font-size: 0.85rem; margin-top: 0.15rem;
}

/* Empty state */
.empty {
    text-align: center; padding: 3rem 1rem;
    background: var(--surface); border: 1px dashed var(--border);
    border-radius: var(--radius-lg);
    display: flex; flex-direction: column; align-items: center; gap: 1rem;
}

/* ---------- Animations ---------- */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(4px); }
    to { opacity: 1; transform: translateY(0); }
}
.fade-in { animation: fadeIn 220ms cubic-bezier(0.4, 0, 0.2, 1); }

@media (prefers-reduced-motion: reduce) {
    .fade-in { animation: none; }
    * { transition-duration: 0.001ms !important; }
}