*{box-sizing:border-box;margin:0;padding:0;font-family:'Segoe UI',sans-serif}
body{display:flex;height:100vh;background:#ffffff;color:#222}
.sidebar{width:250px;background:#4da6ff;color:#fff;display:flex;flex-direction:column}
.logo{padding:1rem;text-align:center;font-size:1.5rem;font-weight:700}
.sidebar nav ul{list-style:none}
.sidebar nav ul li{padding:1rem 1.5rem;cursor:pointer;transition:background .3s}
.sidebar nav ul li:hover,.sidebar nav ul li.active{background:rgba(255,255,255,.2)}
main{flex:1;padding:1.5rem;overflow-y:auto}
.panel{display:none;animation:fade .2s}
.panel.active{display:block}
@keyframes fade{from{opacity:0}to{opacity:1}}
.header{display:flex;justify-content:space-between;align-items:center;margin-bottom:1rem}
#teacherTable{width:100%;border-collapse:collapse}
#teacherTable th,#teacherTable td{border:1px solid #ccc;padding:.5rem;text-align:left}
button{padding:.5rem 1rem;border:none;border-radius:4px;cursor:pointer;background:#4da6ff;color:#fff}
button:hover{opacity:.9}
.modal{position:fixed;top:0;left:0;width:100%;height:100%;background:rgba(0,0,0,.5);display:flex;align-items:center;justify-content:center}
.modal.hidden{display:none}
.modal-content{background:#fff;padding:2rem;border-radius:8px;min-width:300px;max-width:400px;position:relative}
.close{position:absolute;top:.5rem;right:.5rem;font-size:1.5rem;cursor:pointer}
label{display:block;margin-bottom:.5rem}
label input,label select{width:100%;padding:.4rem;margin-top:.2rem;border:1px solid #ccc;border-radius:4px}
@media(max-width:768px){
.sidebar{width:60px}
.sidebar nav ul li{padding:.8rem}
.sidebar nav ul li span{display:none}
}
.panel { display:none; }
.panel.active { display:block; }

.sidebar ul li.active { background:#094c7a; }

.modal { position:fixed; top:0; left:0; width:100%; height:100%; 
         background:rgba(0,0,0,.4); display:flex; align-items:center; 
         justify-content:center; }
.modal-content { background:#fff; padding:20px; border-radius:8px; width:400px; }
.modal.hidden { display:none; }
.close { float:right; font-size:24px; cursor:pointer; }