:root{--ink: #12161c;--ink-faint: #5a6472;--paper: #ffffff;--surface: #f7f8fa;--accent: #2b6ce8;--accent-soft: #eaf0fd;--success: #1f9d55;--success-soft: #e7f6ed;--warning: #d97706;--warning-soft: #fff3df;--border: #e2e5ea;font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,sans-serif}*{box-sizing:border-box}body{margin:0;background:var(--surface);color:var(--ink)}button{font-family:inherit;cursor:pointer;border:none;border-radius:8px;padding:8px 16px;background:var(--accent);color:#fff;font-size:14px}button:disabled{opacity:.5;cursor:default}input,textarea{font-family:inherit;font-size:14px;padding:8px 10px;border:1px solid var(--border);border-radius:8px;width:100%}.centered-page{min-height:100vh;display:flex;align-items:center;justify-content:center}.login-card{display:flex;flex-direction:column;gap:12px;width:320px}.login-card h1{font-size:18px;margin:0 0 8px}.login-card label{display:flex;flex-direction:column;gap:4px;font-size:13px;color:var(--ink-faint)}.card{background:var(--paper);border-radius:12px;padding:20px;box-shadow:0 1px 3px #00000014}.error-text{color:#dc2626;font-size:13px}.app-shell{max-width:900px;margin:0 auto;padding:16px}.app-header{display:flex;align-items:center;justify-content:space-between;padding:12px 0 20px}.brand{font-weight:700}.app-header nav{display:flex;gap:8px}.app-header nav button{background:transparent;color:var(--ink-faint)}.app-header nav button.nav-active{background:var(--accent-soft);color:var(--accent);font-weight:700}.app-header nav button.logout{background:transparent;color:var(--ink-faint)}.class-tabs{display:flex;gap:4px;flex-wrap:wrap;border-bottom:1px solid var(--border);margin-bottom:20px;padding-bottom:0}.class-tab{background:transparent;color:var(--ink-faint);border:none;border-bottom:2px solid transparent;border-radius:0;padding:8px 14px;margin-bottom:-1px}.class-tab-active{color:var(--accent);font-weight:700;border-bottom:2px solid var(--accent)}.search-box{margin-bottom:12px}.count-note{color:var(--ink-faint);font-size:13px;margin:0 0 16px}.lesson-group h3{font-size:14px;color:var(--ink-faint);margin:20px 0 6px}.lesson-list{list-style:none;padding:0;margin:0;background:var(--paper);border-radius:10px;overflow:hidden}.lesson-list li{border-bottom:1px solid var(--border)}.lesson-list li:last-child{border-bottom:none}.link-button{background:transparent;color:var(--accent);padding:10px 14px;width:100%;text-align:left;border-radius:0;font-size:14px}.link-button:hover{background:var(--accent-soft)}.back-link{margin-bottom:12px;padding-left:0}.lesson-meta{color:var(--ink-faint);font-size:13px;margin:0 0 20px}.exercise-card{margin-bottom:16px;border-left:4px solid var(--border)}.exercise-card.approved{border-left-color:var(--success)}.exercise-card.flagged{border-left-color:var(--warning)}.exercise-header{display:flex;align-items:center;gap:10px;margin-bottom:8px}.exercise-id{font-family:ui-monospace,monospace;font-size:12px;color:var(--ink-faint)}.badge{font-size:11px;font-weight:700;padding:2px 8px;border-radius:99px}.badge-ok{background:var(--success-soft);color:var(--success)}.badge-problem{background:var(--warning-soft);color:var(--warning)}.instruction{font-size:16px;font-weight:600;margin:0 0 14px}.field{margin-bottom:12px;font-size:14px}.field-label{display:block;font-size:11px;font-weight:700;text-transform:uppercase;letter-spacing:.4px;color:var(--ink-faint);margin-bottom:4px}.field-value.answer{font-weight:700;color:var(--accent)}.hint-list{margin:0;padding-left:20px}.rubric{background:var(--surface);padding:10px 12px;border-radius:8px}.rubric p,.rubric ul{margin:4px 0}.review-controls{margin-top:16px;padding-top:12px;border-top:1px solid var(--border);display:flex;flex-direction:column;gap:8px}.review-buttons{display:flex;gap:8px}.btn-ok{background:var(--success)}.btn-problem{background:var(--warning)}.problems-header{display:flex;align-items:center;justify-content:space-between;margin-bottom:16px}.problems-table{width:100%;border-collapse:collapse;background:var(--paper);border-radius:10px;overflow:hidden}.problems-table td{padding:10px 12px;border-bottom:1px solid var(--border);font-size:13px;vertical-align:top}.mono{font-family:ui-monospace,monospace}.muted{color:var(--ink-faint);white-space:nowrap}.loading{color:var(--ink-faint);padding:40px;text-align:center}