:root {
    /* DARK THEME (Default) */
    --primary-bg: #0f172a;
    --secondary-bg: #1e293b;
    --accent-color: #3b82f6;
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --border-color: rgba(255, 255, 255, 0.1);
    --error-color: #ef4444;
    --success-color: #10b981;
}

body.light-theme {
    /* LIGHT THEME */
    --primary-bg: #f0f4ff;
    --secondary-bg: #e6edff;
    --accent-color: #2563eb;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --border-color: #9ea3a9;
    --error-color: #dc2626;
    --success-color: #059669;
}

/* --- GLOBAL STYLES --- */
body {
    font-family: 'Inter', sans-serif;
    background: var(--primary-bg);
    color: var(--text-primary);
    margin: 0;
    transition: background-color 0.3s ease, color 0.3s ease;
}

main {
    padding: 2rem 1rem;
}

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

/* --- HEADER / NAVIGATION --- */
.site-header {
    background: var(--secondary-bg);
    border-bottom: 1px solid var(--border-color);
    padding: 1rem 2rem;
    position: sticky;
    top: 0;
    z-index: 2;
}

.header-container {
    max-width: 1400px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.header-left { display: flex; align-items: center; gap: 1.5rem; }
.logo a {
    color: var(--text-primary);
    font-weight: 700;
    font-size: 1.5rem;
    display: flex;
    align-items: center;
    gap: 0.75rem;
}
.logo img { height: 35px; }

.theme-toggle-btn {
    background: none;
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
    width: 40px;
    height: 40px;
    border-radius: 50%;
    cursor: pointer;
    font-size: 1.1rem;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s ease;
}
.theme-toggle-btn:hover { background-color: var(--accent-color); color: white; }

.header-nav ul {
    margin: 0; padding: 0; list-style: none; display: flex; gap: 1rem;
}
.header-nav a {
    padding: 0.5rem 1rem;
    border-radius: 6px;
    font-weight: 500;
    transition: background-color 0.2s ease;
}
.header-nav a:hover { background-color: var(--accent-color); color: white; }
.btn-primary { background-color: var(--accent-color); color: white; }

/* --- FORM STYLES (for login/signup) --- */
.auth-container { max-width: 500px; margin: 3rem auto; }
.auth-card {
    background: var(--secondary-bg);
    padding: 2.5rem;
    border-radius: 16px;
    border: 1px solid var(--border-color);
}
.auth-card h1 { text-align: center; margin-top: 0; }

.form-group { margin-bottom: 1.5rem; }
.form-group label { display: block; font-weight: 500; margin-bottom: 0.5rem; }
.form-input {
    width: 100%;
    padding: 0.75rem 1rem;
    background: var(--primary-bg);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    color: var(--text-primary);
    font-size: 1rem;
    box-sizing: border-box; /* Important for 100% width */
}

.btn-submit {
    width: 100%;
    padding: 0.8rem;
    background: var(--accent-color);
    color: white;
    border: none;
    border-radius: 8px;
    font-weight: 600;
    font-size: 1rem;
    cursor: pointer;
}

.error-message {
    padding: 1rem;
    border-radius: 8px;
    margin-bottom: 1.5rem;
    background: rgba(239, 68, 68, 0.1);
    color: var(--error-color);
    border: 1px solid var(--error-color);
    text-align: center;
}

.auth-switch-link { text-align: center; margin-top: 1.5rem; }