:root {
    --primary: #4CAF50;
    --primary-dark: #388E3C;
    --background: #f4f6f8;
    --surface: #ffffff;
    --text: #333333;
    --text-light: #666666;
    --border: #e0e0e0;
}

body {
    margin: 0;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background-color: var(--background);
    color: var(--text);
}

.screen {
    display: none;
    min-height: 100vh;
}
.screen.active {
    display: flex;
    flex-direction: column;
}

/* Login */
#loginScreen {
    align-items: center;
    justify-content: center;
    background: linear-gradient(135deg, #4CAF50 0%, #2E7D32 100%);
}

.login-box {
    background: var(--surface);
    padding: 2.5rem;
    border-radius: 16px;
    box-shadow: 0 10px 25px rgba(0,0,0,0.2);
    width: 100%;
    max-width: 400px;
    box-sizing: border-box;
}

.login-box h2 {
    margin-top: 0;
    color: var(--primary);
    text-align: center;
    font-size: 1.8rem;
}
.login-box p {
    text-align: center;
    color: var(--text-light);
    margin-bottom: 2rem;
}

.input-group {
    margin-bottom: 1.5rem;
}
.input-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    font-size: 0.9rem;
    color: var(--text);
}
.input-group input {
    width: 100%;
    padding: 0.8rem;
    border: 1px solid var(--border);
    border-radius: 8px;
    box-sizing: border-box;
    font-size: 1rem;
    transition: border-color 0.2s;
}
.input-group input:focus {
    outline: none;
    border-color: var(--primary);
}

.btn {
    padding: 0.8rem 1.5rem;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    font-weight: bold;
    font-size: 1rem;
    transition: all 0.2s;
    width: 100%;
    box-sizing: border-box;
}
.btn.primary {
    background: var(--primary);
    color: white;
}
.btn.primary:hover {
    background: var(--primary-dark);
    transform: translateY(-1px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}
.btn.secondary {
    background: #e0e0e0;
    color: var(--text);
    width: auto;
}
.btn.secondary:hover {
    background: #d5d5d5;
}

/* Dashboard */
header {
    background: var(--surface);
    padding: 1.2rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}
header h2 {
    margin: 0;
    color: var(--primary);
}

main {
    padding: 2rem;
    max-width: 1200px;
    margin: 0 auto;
    width: 100%;
    box-sizing: border-box;
}

.actions {
    margin-bottom: 2rem;
}
.actions .btn {
    width: auto;
}

.data-container {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
    gap: 1.5rem;
}

.classroom-card {
    background: var(--surface);
    padding: 1.5rem;
    border-radius: 12px;
    box-shadow: 0 4px 6px rgba(0,0,0,0.05);
    transition: transform 0.2s;
}
.classroom-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 12px rgba(0,0,0,0.08);
}
.classroom-card h3 {
    margin-top: 0;
    color: var(--text);
    border-bottom: 2px solid var(--primary);
    padding-bottom: 0.8rem;
    margin-bottom: 1rem;
}

.student-list {
    list-style: none;
    padding: 0;
    margin: 0;
}
.student-item {
    padding: 0.8rem 0;
    border-bottom: 1px solid var(--border);
}
.student-item:last-child {
    border-bottom: none;
}
.student-name {
    font-weight: 600;
    color: var(--primary-dark);
}
.student-desk {
    font-size: 0.85rem;
    color: var(--text-light);
    margin-left: 0.5rem;
}
.student-grades {
    margin-top: 0.4rem;
    font-size: 0.9rem;
    color: var(--text);
    background: var(--background);
    padding: 0.5rem;
    border-radius: 6px;
}