:root {
    --bg: linear-gradient(135deg, #667eea, #764ba2);
    --glass: rgba(255,255,255,0.12);
    --border: rgba(255,255,255,0.2);
    --text: #fff;
    --accent1: #00d4ff;
    --accent2: #ff6ec7;
}

body {
    margin: 0;
    font-family: 'Segoe UI', sans-serif;
    background: var(--bg);
    color: var(--text);
}

/* HEADER */
header {
    text-align: center;
    padding: 30px;
}

/* SECTIONS */
.registration-form,
.attendee-list {
    max-width: 600px;
    margin: 20px auto;
    padding: 20px;
    background: var(--glass);
    border-radius: 15px;
    backdrop-filter: blur(12px);
    border: 1px solid var(--border);
    box-shadow: 0 10px 30px rgba(0,0,0,0.4);
    transition: 0.3s;
}

.registration-form:hover,
.attendee-list:hover {
    transform: translateY(-6px);
}

/* FORM */
form {
    display: flex;
    flex-direction: column;
}

input, select {
    margin: 10px 0;
    padding: 10px;
    border-radius: 8px;
    border: none;
    background: rgba(255,255,255,0.2);
    color: white;
}

input::placeholder {
    color: #ddd;
}

/* BUTTON */
button {
    padding: 10px;
    border: none;
    border-radius: 8px;
    background: linear-gradient(45deg, var(--accent1), var(--accent2));
    color: white;
    cursor: pointer;
    transition: 0.3s;
}

button:hover {
    transform: scale(1.05);
}

/* ERROR */
.error {
    color: #ff4d4d;
    font-size: 13px;
    display: none;
}

/* TABLE */
.table-container {
    overflow-x: auto;
}

table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 15px;
    min-width: 500px;
}

th, td {
    padding: 10px;
    border-bottom: 1px solid rgba(255,255,255,0.2);
    white-space: nowrap;
}

th {
    background: rgba(0,0,0,0.3);
}

/* =========================
   BACK BUTTON (3D GLASS)
========================= */
.back-btn {
    position: fixed;
    top: 20px;
    left: 20px;

    display: flex;
    align-items: center;
    gap: 8px;

    padding: 10px 16px;
    border-radius: 12px;

    background: rgba(255,255,255,0.15);
    backdrop-filter: blur(12px);
    border: 1px solid rgba(255,255,255,0.25);

    color: white;
    font-size: 14px;
    cursor: pointer;

    box-shadow: 0 8px 20px rgba(0,0,0,0.3);
    transition: 0.3s ease;

    z-index: 999;
}

.back-btn:hover {
    transform: translateY(-4px) scale(1.05);
    background: rgba(255,255,255,0.25);
    box-shadow: 0 15px 30px rgba(0,0,0,0.5);
}

.back-btn:active {
    transform: scale(0.98);
}