:root {
    --bg: #f4f7f9;
    --card-bg: #ffffff;
    --text-main: #1a1c20;
    --text-muted: #64748b;
    --accent: #4361ee;
    --border: #e2e8f0;
    --shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
}

[data-theme="dark"] {
    --bg: #0f172a;
    --card-bg: #1e293b;
    --text-main: #f1f5f9;
    --text-muted: #94a3b8;
    --border: #334155;
    --shadow: 0 10px 20px rgba(0, 0, 0, 0.3);
}

* { margin: 0; padding: 0; box-sizing: border-box; transition: background 0.3s, color 0.3s, border-color 0.3s; }
body { background: var(--bg); color: var(--text-main); font-family: 'Plus Jakarta Sans', sans-serif; line-height: 1.5; }

.wrapper { max-width: 500px; margin: 0 auto; padding: 40px 20px; }

/* Navigation & Theme Toggle */
nav { display: flex; justify-content: space-between; align-items: center; margin-bottom: 30px; }
.back-link { text-decoration: none; color: var(--accent); font-weight: 600; font-size: 0.9rem; }

#theme-toggle {
    background: var(--card-bg); border: 1px solid var(--border); color: var(--text-main);
    width: 40px; height: 40px; border-radius: 12px; cursor: pointer;
    display: flex; align-items: center; justify-content: center; box-shadow: var(--shadow);
}

/* Header */
header { text-align: center; margin-bottom: 30px; }
header h1 { font-size: 2rem; letter-spacing: -1px; margin-bottom: 5px; }
header p { color: var(--text-muted); font-size: 0.95rem; }

/* Main Card */
.card {
    background: var(--card-bg); border: 1px solid var(--border);
    padding: 30px; border-radius: 24px; box-shadow: var(--shadow);
}

.input-group label, .select-group label {
    display: block; font-size: 0.75rem; font-weight: 700;
    text-transform: uppercase; color: var(--text-muted); margin-bottom: 8px;
}

input, select {
    width: 100%; background: var(--bg); border: 1px solid var(--border);
    padding: 14px 15px; border-radius: 12px; color: var(--text-main);
    font-family: inherit; font-size: 1.1rem; outline: none;
}
input:focus, select:focus { border-color: var(--accent); }

/* Currency Select Row */
.currency-row {
    display: flex; align-items: flex-end; gap: 15px; margin: 25px 0;
}
.select-group { flex: 1; }

#swap-btn {
    background: var(--bg); color: var(--text-main); border: 1px solid var(--border);
    width: 45px; height: 45px; border-radius: 12px; cursor: pointer;
    display: flex; align-items: center; justify-content: center; margin-bottom: 2px;
}
#swap-btn:hover { background: var(--accent); color: white; border-color: var(--accent); }

/* Result Area */
.result-area {
    margin-top: 30px; padding-top: 25px; border-top: 1px solid var(--border);
    text-align: center; background: var(--bg); border-radius: 16px; padding: 25px 15px;
}
.result-label { font-size: 0.8rem; color: var(--text-muted); text-transform: uppercase; font-weight: 700; margin-bottom: 5px; }
#result-val { font-size: 2.2rem; font-weight: 700; color: var(--accent); word-break: break-all; }
#rate-text { font-size: 0.85rem; color: var(--text-muted); margin-top: 10px; font-weight: 600; }

.update-note { text-align: center; margin-top: 20px; font-size: 0.8rem; color: var(--text-muted); }

/* Mobile Stack View */
@media (max-width: 450px) {
    .currency-row { flex-direction: column; align-items: stretch; gap: 10px; }
    #swap-btn { align-self: center; transform: rotate(90deg); margin: 5px 0; }
    #swap-btn:hover { transform: rotate(90deg) scale(1.05); }
    .card { padding: 20px; }
    #result-val { font-size: 1.8rem; }
}