:root {
    --bg-color: #f5f5f7;
    --card-bg: #ffffff;
    --text-main: #1d1d1f;
    --text-secondary: #86868b;
    --blue: #0071e3;
    --blue-hover: #0077ED;
    --border-radius: 18px;
}

* { box-sizing: border-box; margin: 0; padding: 0; font-family: -apple-system, BlinkMacSystemFont, sans-serif; }
body { background-color: var(--bg-color); color: var(--text-main); padding-bottom: 50px; }

/* Header & Tabs */
.header { text-align: center; padding: 40px 20px 20px; }
.header img { width: 100px; height: 100px; border-radius: 50%; box-shadow: 0 4px 12px rgba(0,0,0,0.1); }
.header h1 { font-size: 28px; font-weight: 700; margin-top: 16px; }
.header p { color: var(--text-secondary); font-size: 15px; margin-top: 8px; }
.social-btn { display: inline-block; background: #000; color: #fff; padding: 12px 24px; border-radius: 30px; text-decoration: none; font-weight: 600; margin-top: 20px; font-size: 14px; }

.tabs { display: flex; justify-content: center; gap: 20px; margin: 20px 0 30px; }
.tab-btn { background: transparent; border: none; font-size: 18px; font-weight: 600; color: var(--text-secondary); cursor: pointer; padding-bottom: 5px; }
.tab-btn.active { color: var(--text-main); border-bottom: 2px solid var(--text-main); }
.section { display: none; } .section.active { display: block; }

/* Home Cards */
.list-container { padding: 0 20px; display: grid; gap: 16px; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); max-width: 600px; margin: 0 auto;}
.card { background: var(--card-bg); border-radius: var(--border-radius); padding: 24px; box-shadow: 0 4px 16px rgba(0,0,0,0.04); text-align: center;}
.card h3 { font-size: 18px; margin-bottom: 10px; }
.card p { font-size: 14px; color: var(--text-secondary); margin-bottom: 20px; }
.btn-primary { width: 100%; background: var(--blue); color: white; border: none; padding: 14px; border-radius: 20px; font-size: 15px; font-weight: 600; cursor: pointer; transition: background 0.2s; }
.btn-primary:hover { background: var(--blue-hover); }

/* --- GIAO DIỆN ĐA NHIỆM (APP SWITCHER) --- */
.switcher-overlay {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%;
    background: #1c1c1e; /* Màu nền đen iOS */
    z-index: 500; display: none; flex-direction: column;
}
.switcher-header { display: flex; justify-content: space-between; align-items: center; padding: 40px 20px 20px; color: white; }
.switcher-header h2 { font-size: 20px; font-weight: 600; }
.close-switcher { background: #3a3a3c; color: white; border: none; border-radius: 15px; width: 30px; height: 30px; font-weight: bold; cursor: pointer; display: flex; align-items: center; justify-content: center;}

.multitasking-container {
    flex: 1; display: flex; align-items: center; overflow-x: auto; scroll-snap-type: x mandatory; padding: 0 20px; gap: 20px;
    scrollbar-width: none;
}
.multitasking-container::-webkit-scrollbar { display: none; }
.hint-text-switcher { text-align: center; color: #86868b; font-size: 13px; padding-bottom: 40px; }

.task-card {
    scroll-snap-align: center; min-width: 75vw; max-width: 320px; height: 60vh; max-height: 450px;
    border-radius: 30px; padding: 24px; display: flex; flex-direction: column; justify-content: space-between;
    box-shadow: 0 10px 30px rgba(0,0,0,0.5); color: white; cursor: pointer; transition: transform 0.2s;
}
.task-card:active { transform: scale(0.95); }
.task-icon { width: 45px; height: 45px; background: rgba(255,255,255,0.3); border-radius: 12px; display: flex; align-items: center; justify-content: center; font-size: 20px; }
.task-info h3 { font-size: 24px; margin-bottom: 8px; font-weight: 700; line-height: 1.2;}
.task-info p { font-size: 15px; opacity: 0.9; }

/* --- MODAL XÁC MINH --- */
.modal-overlay {
    display: none; position: fixed; top: 0; left: 0; right: 0; bottom: 0;
    background: rgba(0,0,0,0.5); backdrop-filter: blur(5px); z-index: 1000;
    align-items: center; justify-content: center; padding: 20px;
}
.modal-content {
    background: var(--card-bg); width: 100%; max-width: 400px; border-radius: 24px; padding: 24px;
    position: relative; box-shadow: 0 20px 40px rgba(0,0,0,0.2); animation: slideUp 0.3s ease-out;
}
@keyframes slideUp { from { transform: translateY(20px); opacity: 0; } to { transform: translateY(0); opacity: 1; } }
.close-btn { position: absolute; top: 16px; right: 16px; background: #e5e5ea; border: none; width: 30px; height: 30px; border-radius: 15px; font-weight: bold; color: var(--text-secondary); cursor: pointer; }
.modal-title { font-size: 18px; font-weight: 700; margin-bottom: 20px; text-align: center;}
.step-title { font-size: 15px; margin-bottom: 12px; font-weight: 600; }
.btn-shopee { background: #ee4d2d; color: white; border: none; padding: 14px; border-radius: 12px; font-size: 15px; font-weight: 600; cursor: pointer; width: 100%; margin-bottom: 20px; }

#step2 { display: none; }
.product-list { margin-bottom: 20px; font-size: 15px; line-height: 1.8; font-weight: 500; color: #333;}
.answer-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 12px; }
.btn-answer { background: #f2f2f7; border: none; padding: 14px; border-radius: 12px; font-size: 16px; font-weight: 700; cursor: pointer; color: #1d1d1f;}
.btn-answer:active { background: #e5e5ea; }