:root {
    color-scheme: light dark;
    font-family: system-ui, -apple-system, sans-serif;
    -webkit-text-size-adjust: 100%;
    --gap: 1rem;
    --radius: 0.75rem;
    --accent: #3b6ef5;
    --bg: #ffffff;
    --fg: #14161a;
}

@media (prefers-color-scheme: dark) {
    :root {
        --accent: #6b93ff;
        --bg: #14161a;
        --fg: #eceef2;
    }
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    background: var(--bg);
    color: var(--fg);
}

#app {
    min-height: 100dvh;
    display: flex;
    justify-content: center;
}

.screen {
    width: 100%;
    max-width: 32rem;
    padding: calc(var(--gap) + env(safe-area-inset-top)) var(--gap)
             calc(var(--gap) + env(safe-area-inset-bottom));
    display: flex;
    flex-direction: column;
    gap: var(--gap);
}

h1 {
    margin: 0;
    font-size: 1.75rem;
}

.muted {
    opacity: 0.6;
    margin: 0;
}

.top-bar {
    display: flex;
}

button {
    font: inherit;
    cursor: pointer;
    border: none;
    border-radius: var(--radius);
    padding: 0.85rem 1rem;
    background: color-mix(in srgb, currentColor 8%, transparent);
    color: inherit;
}

button:active {
    transform: translateY(1px);
}

.link {
    background: none;
    padding: 0.35rem 0;
    opacity: 0.8;
}

.deck-list {
    display: flex;
    flex-direction: column;
    gap: 0.6rem;
}

.contribute-link {
    margin-top: 0.25rem;
    align-self: flex-start;
    text-decoration: none;
    color: inherit;
}

.deck-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    text-align: left;
    padding: 1rem;
}

.deck-title {
    font-weight: 600;
}

.deck-count {
    opacity: 0.6;
    font-size: 0.9rem;
}

.toggle-on {
    background: color-mix(in srgb, var(--accent) 25%, transparent);
}

.primary {
    background: var(--accent);
    color: #fff;
    font-weight: 600;
    padding: 1rem;
}

/* --- Study --- */
.study-bar {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.progress {
    opacity: 0.6;
    font-variant-numeric: tabular-nums;
}

.card {
    flex: 1;
    min-height: 55dvh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 0.75rem;
    padding: 1.5rem;
    border-radius: 1rem;
    cursor: pointer;
    user-select: none;
    text-align: center;
    background: color-mix(in srgb, currentColor 6%, transparent);
    border: 1px solid color-mix(in srgb, currentColor 12%, transparent);
    animation: flip-in 0.18s ease-out;
}

@keyframes flip-in {
    from { transform: rotateY(-90deg); opacity: 0.3; }
    to   { transform: rotateY(0); opacity: 1; }
}

.card-side {
    text-transform: uppercase;
    letter-spacing: 0.08em;
    font-size: 0.7rem;
    opacity: 0.5;
}

.card.is-back .card-side {
    color: var(--accent);
    opacity: 0.9;
}

.card-text {
    font-size: clamp(1.75rem, 8vw, 2.75rem);
    font-weight: 600;
    line-height: 1.2;
}

.card-hint {
    font-size: 0.8rem;
}

.nav {
    display: flex;
    gap: 0.6rem;
}

.nav-btn {
    flex: 1;
    padding: 1rem;
}

.nav-btn:disabled {
    opacity: 0.35;
    cursor: default;
}

/* --- Complete --- */
.complete {
    flex: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 0.75rem;
    text-align: center;
}

.complete .primary {
    margin-top: 0.5rem;
    min-width: 12rem;
}