:root {
    --bg-color: #f0f4f8;
    --text-main: #1e293b;
    --text-light: #64748b;
    --border-color: #e2e8f0;
    --card-bg: #ffffff;
}

/* Default (Student) theme — swapped by JS when the Instructor tab is active */
body {
    --brand-gradient: linear-gradient(135deg, #6366f1 0%, #a855f7 100%);
    --brand-color: #6366f1;
    --brand-shadow: rgba(99, 102, 241, 0.18);
}

body.theme-instructor {
    --brand-gradient: linear-gradient(135deg, #1e3a8a 0%, #3b82f6 100%);
    --brand-color: #3b82f6;
    --brand-shadow: rgba(59, 130, 246, 0.18);
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 24px;
    font-family: 'Plus Jakarta Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-color);
    color: var(--text-main);
    transition: background 0.3s ease;
}

.auth-card {
    width: 100%;
    max-width: 420px;
    background: var(--card-bg);
    border-radius: 20px;
    box-shadow: 0 20px 45px rgba(15, 23, 42, 0.08);
    padding: 40px;
}

.auth-brand {
    text-align: center;
    margin-bottom: 28px;
}

.auth-brand .auth-logo {
    width: 56px;
    height: 56px;
    border-radius: 16px;
    background: var(--brand-gradient);
    color: #fff;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    font-size: 24px;
    margin-bottom: 14px;
    transition: background 0.3s ease;
    box-shadow: 0 10px 25px var(--brand-shadow);
}

.auth-brand h1 {
    font-size: 19px;
    font-weight: 800;
    margin: 0 0 4px;
    letter-spacing: -0.01em;
}

.auth-brand p {
    font-size: 13px;
    color: var(--text-light);
    margin: 0;
}

/* Tab switcher */
.auth-tabs {
    display: flex;
    background: #f1f5f9;
    border-radius: 14px;
    padding: 4px;
    margin-bottom: 24px;
}

.auth-tab {
    flex: 1;
    border: none;
    background: transparent;
    padding: 10px 12px;
    border-radius: 10px;
    font-size: 13px;
    font-weight: 700;
    color: var(--text-light);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    transition: all 0.25s ease;
}

.auth-tab.active {
    background: var(--brand-gradient);
    color: #fff;
    box-shadow: 0 6px 16px var(--brand-shadow);
}

/* Form */
.auth-field {
    margin-bottom: 18px;
}

.auth-field label {
    display: block;
    font-size: 13px;
    font-weight: 600;
    margin-bottom: 6px;
    color: var(--text-main);
}

.auth-input-wrap {
    position: relative;
}

.auth-input-wrap i {
    position: absolute;
    left: 14px;
    top: 50%;
    transform: translateY(-50%);
    color: #94a3b8;
    font-size: 14px;
}

.auth-input-wrap input {
    width: 100%;
    padding: 12px 14px 12px 40px;
    border: 1px solid var(--border-color);
    border-radius: 10px;
    font-size: 14px;
    outline: none;
    transition: all 0.25s ease;
    background: #fff;
    color: var(--text-main);
}

.auth-input-wrap input:focus {
    border-color: var(--brand-color);
    box-shadow: 0 0 0 3px var(--brand-shadow);
}

.auth-options {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 22px;
    font-size: 13px;
}

.auth-options label {
    display: flex;
    align-items: center;
    gap: 6px;
    color: var(--text-light);
    cursor: pointer;
}

.auth-options a {
    color: var(--brand-color);
    text-decoration: none;
    font-weight: 600;
    transition: color 0.25s ease;
}

.auth-submit {
    width: 100%;
    border: none;
    border-radius: 10px;
    padding: 13px;
    font-size: 14px;
    font-weight: 700;
    color: #fff;
    background: var(--brand-gradient);
    box-shadow: 0 10px 25px var(--brand-shadow);
    cursor: pointer;
    transition: all 0.25s ease;
}

.auth-submit:hover {
    transform: translateY(-2px);
}

.auth-alert {
    background: #fef2f2;
    color: #b91c1c;
    border-radius: 10px;
    padding: 10px 14px;
    font-size: 13px;
    margin-bottom: 18px;
}

.auth-footer {
    text-align: center;
    font-size: 12px;
    color: var(--text-light);
    margin-top: 24px;
}

/* Instructor Agreement gate (section-by-section read + accept) */
.agreement-card {
    max-width: 640px;
}

.agreement-progress {
    margin-bottom: 22px;
}

.agreement-progress-track {
    height: 6px;
    border-radius: 999px;
    background: #f1f5f9;
    overflow: hidden;
}

.agreement-progress-fill {
    height: 100%;
    background: var(--brand-gradient);
    border-radius: 999px;
    transition: width 0.25s ease;
}

.agreement-progress-label {
    display: block;
    margin-top: 8px;
    font-size: 12px;
    font-weight: 600;
    color: var(--text-light);
    text-align: center;
}

.agreement-section-title {
    font-size: 16px;
    font-weight: 700;
    margin: 0 0 12px;
    color: var(--text-main);
}

.agreement-section-body {
    font-size: 14px;
    line-height: 1.7;
    color: var(--text-main);
    max-height: 320px;
    overflow-y: auto;
    padding-right: 6px;
    margin-bottom: 8px;
}

.agreement-accept-row {
    margin-top: 18px;
    padding-top: 18px;
    border-top: 1px solid var(--border-color);
}

.agreement-accept-check {
    display: flex;
    align-items: flex-start;
    gap: 10px;
    font-size: 13px;
    font-weight: 600;
    color: var(--text-main);
    cursor: pointer;
}

.agreement-accept-check input {
    margin-top: 3px;
    flex-shrink: 0;
}

.agreement-nav {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-top: 24px;
}

.agreement-nav .auth-submit {
    width: auto;
    flex: 1;
}

.agreement-btn-back {
    border: 1px solid var(--border-color);
    background: #fff;
    color: var(--text-main);
    border-radius: 10px;
    padding: 13px 18px;
    font-size: 14px;
    font-weight: 700;
    cursor: pointer;
    transition: all 0.25s ease;
}

.agreement-btn-back:hover {
    background: #f8fafc;
}

.agreement-btn-accept:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none;
}