:root {
    --primary: #2563eb;
    --primary-dark: #1d4ed8;
    --bg-gray: #f8fafc;
    --card-bg: #ffffff;
    --text-main: #1e293b;
    --text-muted: #64748b;
    --border-color: #e2e8f0;
    --success: #16a34a;
}

* { box-sizing: border-box; margin: 0; padding: 0; font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; }

body { background-color: var(--bg-gray); color: var(--text-main); display: flex; flex-direction: column; min-height: 100vh; }

header { background: #0f172a; color: white; padding: 1rem 2rem; display: flex; justify-content: space-between; align-items: center; }
header a { color: white; text-decoration: none; margin-left: 15px; font-weight: 500; }
header .logo { font-size: 1.25rem; font-weight: bold; color: #38bdf8; }

.container { width: 90%; max-width: 1100px; margin: 2rem auto; flex: 1; }

.card { background: var(--card-bg); padding: 2rem; border-radius: 8px; box-shadow: 0 4px 6px -1px rgba(0,0,0,0.1); border: 1px solid var(--border-color); margin-bottom: 1.5rem; }

.btn { display: inline-block; padding: 0.6rem 1.2rem; background: var(--primary); color: white; border: none; border-radius: 6px; cursor: pointer; text-decoration: none; font-weight: 600; font-size: 0.9rem; }
.btn:hover { background: var(--primary-dark); }
.btn-secondary { background: #64748b; }
.btn-secondary:hover { background: #475569; }
.btn-success { background: var(--success); }

form .form-group { margin-bottom: 1.2rem; }
form label { display: block; margin-bottom: 0.4rem; font-weight: 600; color: var(--text-main); }
form input[type="text"], form input[type="email"], form input[type="password"], form select, form textarea {
    width: 100%; padding: 0.75rem; border: 1px solid var(--border-color); border-radius: 6px; font-size: 1rem;
}

.auth-box { max-width: 420px; margin: 3rem auto; }

/* Grid & List Styles */
.grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); gap: 1.5rem; }
.lesson-list { list-style: none; }
.lesson-item { background: #fff; padding: 1rem 1.5rem; border: 1px solid var(--border-color); border-radius: 6px; margin-bottom: 0.75rem; display: flex; justify-content: space-between; align-items: center; }
.lesson-item.completed { border-left: 4px solid var(--success); }

/* Progress Bar */
.progress-bar-bg { width: 100%; background: #e2e8f0; height: 12px; border-radius: 6px; overflow: hidden; margin: 10px 0; }
.progress-bar-fill { background: var(--success); height: 100%; width: 0%; transition: width 0.3s ease; }

/* Quiz Styling */
.quiz-option { display: block; background: #f1f5f9; padding: 0.8rem 1rem; margin: 0.5rem 0; border-radius: 6px; cursor: pointer; border: 1px solid var(--border-color); }
.quiz-option:hover { background: #e2e8f0; }