:root{
  --bg:#eef2fb;
  --glass: rgba(255,255,255,0.7);
  --muted:#6b7280;
  --accent1: #6a5af9;
  --accent2: #8a4df5;
  --radius: 14px;
  --card-shadow: 0 10px 30px rgba(20,20,50,0.06);
  --glass-border: rgba(255,255,255,0.6);
}

*{box-sizing:border-box}
html,body{height:100%}
body{
  margin:0;
  font-family: Inter, system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial;
  background: linear-gradient(180deg, #eef2fb 0%, #f7f9ff 100%);
  color: #111827;
  -webkit-font-smoothing:antialiased;
  -moz-osx-font-smoothing:grayscale;
}

/* APP LAYOUT */
.app{display:flex;min-height:100vh;gap:22px;padding:22px}

/* SIDEBAR */
.sidebar{
  width:260px;
  border-radius:var(--radius);
  background: linear-gradient(180deg, rgba(255,255,255,0.7), rgba(255,255,255,0.58));
  padding:18px;
  box-shadow: var(--card-shadow);
  display:flex;flex-direction:column;justify-content:space-between;
  backdrop-filter: blur(8px) saturate(120%);
  border: 1px solid var(--glass-border);
  transition: width .28s ease;
}
.brand{display:flex;gap:12px;align-items:center}
.logo{
  width:56px;height:56px;border-radius:12px;
  background: linear-gradient(135deg,var(--accent1),var(--accent2));
  color:white;display:flex;align-items:center;justify-content:center;font-weight:800;font-size:20px;
  box-shadow: 0 6px 18px rgba(106,90,249,0.18), inset 0 -2px 6px rgba(0,0,0,0.06);
}
.brand-text .title{font-weight:700}
.brand-text .subtitle{font-size:12px;color:var(--muted)}

/* NAV */
.nav{display:flex;flex-direction:column;gap:6px;margin-top:18px}
.nav-item{
  display:flex;align-items:center;gap:10px;padding:10px 12px;border-radius:10px;border:none;background:transparent;color: #222;
  cursor:pointer;font-weight:600;font-size:14px;text-align:left;
}
.nav-item i{width:18px;text-align:center;color:var(--accent1)}
.nav-item:hover{background:rgba(106,90,249,0.06)}
.nav-item.active{background:linear-gradient(90deg, rgba(106,90,249,0.12), rgba(138,77,245,0.06));box-shadow:inset 0 1px 0 rgba(255,255,255,0.4)}

/* sidebar bottom */
.sidebar-bottom{display:flex;align-items:center;gap:8px;justify-content:space-between;margin-top:20px}
.role-toggle label{font-size:12px;color:var(--muted);display:block;margin-bottom:6px}
.role-toggle select{padding:8px;border-radius:10px;border:1px solid #e8e8ef;background:white}
.collapse{background:transparent;border:none;color:var(--muted);font-size:18px;cursor:pointer}

/* MAIN */
.main{flex:1;display:flex;flex-direction:column;gap:18px}
.topbar{
  display:flex;justify-content:space-between;align-items:center;padding:10px 16px;border-radius:12px;
  background: linear-gradient(90deg, rgba(255,255,255,0.6), rgba(255,255,255,0.5));
  border:1px solid var(--glass-border);box-shadow:var(--card-shadow);backdrop-filter: blur(6px);
}
.search{position:relative;flex:1;max-width:640px}
.search input{width:100%;padding:12px 40px 12px 14px;border-radius:10px;border:1px solid #e6e9f2;background:white}
.search i{position:absolute;right:12px;top:10px;color:var(--muted)}
.top-actions{display:flex;align-items:center;gap:12px}
.clock{color:var(--muted);font-weight:600}
.avatar{width:40px;height:40px;border-radius:10px;background:linear-gradient(135deg,#fff,#f3f4ff);display:flex;align-items:center;justify-content:center;color:var(--accent1);font-size:18px}

/* CONTENT */
.content{padding:6px 0}
.page{display:none}
.page.active{display:block}
.grid{display:grid;grid-template-columns:repeat(3,1fr);gap:18px;margin-bottom:18px}
.card{background:white;border-radius:14px;padding:18px;box-shadow: var(--card-shadow);border:1px solid rgba(0,0,0,0.03)}
.card.large{padding:14px}
.card-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:12px}
.card-header h2{margin:0}
.btn{padding:8px 12px;border-radius:10px;border:none;background:#eef0ff;color:var(--accent1);cursor:pointer;font-weight:700}
.btn.primary{background:linear-gradient(90deg,var(--accent1),var(--accent2));color:white;box-shadow:0 6px 18px rgba(106,90,249,0.18)}
.btn.danger{background:#ffdede;color:#c33;border-radius:10px}

/* summary card */
.summary{display:flex;flex-direction:column;gap:10px}
.card-top{display:flex;justify-content:space-between;align-items:center}
.card-value{font-size:28px;font-weight:800}

/* recent list */
.recent-list{display:flex;flex-direction:column;gap:10px}
.recent-item{display:flex;justify-content:space-between;align-items:center;padding:12px;border-radius:12px;background:linear-gradient(180deg,#fff,#fafcff);border:1px solid rgba(106,90,249,0.06)}
.recent-left{display:flex;gap:12px;align-items:center}
.tag{padding:6px 10px;border-radius:8px;font-weight:700;color:white}
.tag.pending{background:gray}
.tag.submitted{background:#f5a623}
.tag.checked{background:#2ecc71}
.muted{color:var(--muted);font-size:13px}

/* HW container */
.upload-panel{display:flex;gap:10px;flex-wrap:wrap;align-items:center;margin-bottom:12px}
.upload-panel input[type="text"], .upload-panel input[type="date"]{padding:10px;border-radius:10px;border:1px solid #e6e9f2;background:white}
.upload-panel input[type="file"]{padding:6px}
.hw-container{overflow:auto}
.table{width:100%;border-collapse:collapse}
.table th, .table td{padding:12px;border-bottom:1px solid #f1f2f8;text-align:left}
.table th{background:linear-gradient(90deg,#fbfaff,#f6f6ff)}
.table td a{color:var(--accent1);text-decoration:none}

/* card-mode for assignments */
.cards-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:14px}
.hw-card{border-radius:12px;padding:14px;background:linear-gradient(180deg,#fff,#fbfbff);box-shadow:0 6px 20px rgba(20,20,50,0.04);border:1px solid rgba(106,90,249,0.04)}
.hw-card h3{margin:0;font-size:16px}
.hw-meta{display:flex;gap:10px;align-items:center;margin-top:10px}
.small{font-size:12px;padding:6px 8px;border-radius:8px;background:#f2f4ff;color:var(--accent1);}

/* students */
.student-list{display:flex;gap:10px;flex-wrap:wrap}
.student-pill{background:#fff;border:1px solid #f0f0f6;padding:8px 10px;border-radius:999px;box-shadow:0 4px 12px rgba(0,0,0,0.03)}

/* footer */
.footer{text-align:center;color:var(--muted);padding:10px 0}

/* modal */
.modal{position:fixed;inset:0;display:flex;align-items:center;justify-content:center;background:rgba(5,6,12,0.4);z-index:50}
.modal.hidden{display:none}
.modal-card{width:720px;max-width:94%;background:white;border-radius:12px;padding:18px;position:relative}
.modal-close{position:absolute;right:12px;top:12px;border:none;background:transparent;font-size:18px;cursor:pointer}

/* small screens */
@media (max-width:900px){
  .grid{grid-template-columns:repeat(1,1fr)}
  .cards-grid{grid-template-columns:repeat(1,1fr)}
  .sidebar{width:72px}
  .brand-text{display:none}
  .nav-item span{display:none}
  .app{padding:12px}
  .search input{max-width:360px}
}