:root {
    --primary: #e94560;
    --bg: #1a1a2e;
    --card: #16213e;
    --text: #ffffff;
    --accent: #4ecca3;
    --error: #ff4d4d;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: var(--bg);
    color: var(--text);
    margin: 0;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

header {
    background: var(--card);
    padding: 20px;
    text-align: center;
    border-bottom: 3px solid var(--primary);
}

main {
    flex: 1;
    padding: 20px;
    max-width: 900px;
    margin: 0 auto;
    width: 100%;
}

.home-hero {
    text-align: center;
    padding: 50px 20px;
}

.login-card, .lesson-card, .report-card, .filter-bar {
    background: var(--card);
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.3);
    margin-bottom: 20px;
}

.filter-bar {
    display: flex;
    justify-content: center;
    gap: 10px;
    flex-wrap: wrap;
    align-items: center;
}

.report-item {
    background: var(--card);
    padding: 15px;
    border-radius: 8px;
    margin-bottom: 10px;
    border-left: 5px solid var(--primary);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.grade-badge {
    font-weight: bold;
    color: var(--primary);
    font-size: 1.2em;
}

h1, h2, h3 {
    color: var(--primary);
}

.error {
    background: rgba(255, 77, 77, 0.2);
    border: 1px solid var(--error);
    padding: 10px;
    border-radius: 5px;
    margin-bottom: 15px;
}

form label, .filter-bar label {
    display: block;
    margin: 5px 0;
}

form input[type="text"],
form input[type="password"],
form input[type="email"],
select {
    padding: 10px;
    border-radius: 5px;
    border: 1px solid #0f3460;
    background: #0f3460;
    color: white;
}

button, .btn-start, .btn-login, .btn-submit, .btn-view {
    padding: 10px 20px;
    border-radius: 5px;
    border: none;
    cursor: pointer;
    font-weight: bold;
    background: var(--primary);
    color: white;
    text-decoration: none;
    display: inline-block;
}

.btn-help {
    background: var(--accent);
    color: #1a1a2e;
    font-size: 0.8em;
}

.problem-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 20px;
    list-style-type: none;
    padding: 0;
}

.question-block {
    padding: 20px;
    border-bottom: 1px solid #0f3460;
}

.explanation-box {
    margin-top: 10px;
    padding: 15px;
    background: rgba(255,255,255,0.05);
    border-left: 4px solid var(--primary);
    font-style: italic;
}

.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0,0,0,0);
    border: 0;
}

footer {
    background: var(--card);
    padding: 20px;
    text-align: center;
    font-size: 0.9em;
    border-top: 1px solid #0f3460;
    margin-top: auto;
}