body {
  font-family: 'Inter', sans-serif;
  background: linear-gradient(180deg, #f9fbff 0%, #eef3fb 100%);
  margin: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  color: #1a1a1a;
}

.merge-container {
  background: #fff;
  border-radius: 24px;
  box-shadow: 0 12px 35px rgba(0, 0, 0, 0.1);
  padding: 40px 50px; /* Giảm padding một chút */
  max-width: 800px;
  width: 90%;
  text-align: center;
  margin: 20px auto; /* Giảm margin */
  transition: transform 0.3s ease;
  flex-grow: 1; /* Thêm để chiếm không gian */
  overflow-y: auto; /* Cho phép cuộn bên trong */
  display: flex; /* Thêm để căn giữa nội dung bên trong */
  flex-direction: column; /* Thêm */
  justify-content: center; /* Thêm */
}

.merge-container:hover {
  transform: translateY(-5px);
}

h1 {
  font-size: 2.5rem;
  font-weight: 700;
  margin-bottom: 10px;
  color: #111827;
}

p {
  font-size: 1.1rem;
  color: #555;
  margin-bottom: 40px;
}

.upload-box {
  border: 2px dashed #3b82f6;
  border-radius: 16px;
  background-color: #f0f7ff;
  padding: 40px 30px;
  transition: all 0.3s ease;
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 20px;
}

.upload-box.drag-over {
  background-color: #e6f0ff;
  border-color: #2563eb;
  transform: scale(1.02);
  box-shadow: 0 8px 25px rgba(37,99,235,0.15);
}

.upload-box.drag-over .drop-text {
  color: #2563eb;
}

.select-btn {
  background: linear-gradient(45deg, #2563eb, #3b82f6);
  color: #fff;
  font-weight: 600;
  border: none;
  padding: 16px 35px;
  border-radius: 12px;
  cursor: pointer;
  font-size: 1.1rem;
  transition: all 0.3s ease;
  z-index: 2;
}

.select-btn:hover {
  background: linear-gradient(45deg, #1d4ed8, #2563eb);
  transform: translateY(-2px);
  box-shadow: 0 5px 15px rgba(37,99,235,0.3);
}

.drag-text {
  font-size: 1rem;
  color: #4b5563;
  margin-top: 10px;
}

.drop-text {
  font-size: 1rem;
  color: #4b5563;
  margin-top: 15px;
  text-align: center;
  font-weight: 500;
}

.file-list {
  width: 100%;
  margin-top: 20px;
}

.file-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 10px 15px;
  background: #f3f4f6;
  border-radius: 8px;
  margin-bottom: 8px;
}

.file-item span {
  color: #374151;
  font-size: 0.95rem;
}

.file-item small {
  color: #6b7280;
}

.remove-btn {
  background: #ef4444;
  color: white;
  border: none;
  border-radius: 6px;
  width: 24px;
  height: 24px;
  font-size: 16px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.2s ease;
}

.remove-btn:hover {
  background: #dc2626;
  transform: scale(1.1);
}

.upload-btn {
  background: linear-gradient(45deg, #2563eb, #3b82f6);
  color: #fff;
  font-weight: 600;
  border: none;
  padding: 16px 35px;
  border-radius: 12px;
  cursor: pointer;
  font-size: 1.1rem;
  transition: all 0.3s ease;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  width: 80%;
  max-width: 300px;
}

.upload-btn:hover {
  background: linear-gradient(45deg, #1d4ed8, #2563eb);
  transform: translateY(-2px);
  box-shadow: 0 5px 15px rgba(37,99,235,0.3);
}

.hint {
  margin-top: 15px;
  color: #6b7280;
  font-size: 0.95rem;
}

.hint-text {
    font-size: 0.8rem;
    color: #6b7280;
    margin-top: -10px;
    margin-bottom: 10px;
}

/* Loading styles */
.upload-box.loading {
    position: relative;
    pointer-events: none; /* khi loading, chặn thao tác tiếp */
}

.upload-box.loading .select-btn,
.upload-box.loading .drop-text,
.upload-box.loading .drag-text, /* ẩn cả drag-text nếu có */
.upload-box.loading .file-list,
.upload-box.loading .hint-text {
    visibility: hidden;
}

.loading-bar {
    width: 60%;
    height: 4px;
    background-color: #e2e8f0;
    border-radius: 2px;
    overflow: hidden;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    z-index: 5; /* nổi trên mọi lớp trong upload-box */
}

.loading-bar::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    height: 100%;
    width: 40%;
    background: linear-gradient(90deg, #2563eb, #3b82f6);
    animation: loading 1s infinite ease-in-out;
}

.loading-text {
    position: absolute;
    top: calc(50% + 20px);
    left: 50%;
    transform: translateX(-50%);
    color: #2563eb;
    font-size: 1rem;
    font-weight: 500;
    z-index: 5; /* nổi trên mọi lớp trong upload-box */
}

@keyframes loading {
    0% { transform: translateX(-100%); }
    100% { transform: translateX(350%); }
}

.next-btn {
    background: linear-gradient(45deg, #10b981, #059669);
    color: white;
    border: none;
    padding: 12px 30px;
    border-radius: 8px;
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    margin-top: 20px;
    transition: all 0.3s ease;
    display: none;
}

.next-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(5, 150, 105, 0.4);
}

.file-info {
    margin-top: 20px;
    text-align: left;
}

.file-info ul {
    list-style: none;
    padding: 0;
}

.file-info li {
    padding: 8px 12px;
    background: #f3f4f6;
    margin-bottom: 8px;
    border-radius: 6px;
    font-size: 0.9rem;
    color: #374151;
}

/* --- Responsive Styles for Mobile --- */
@media (max-width: 768px) {
    .merge-container {
        padding: 30px 20px;
        width: 95%;
        margin: 20px auto; /* Điều chỉnh margin */
        justify-content: flex-start; /* Cho nội dung bắt đầu từ trên */
    }

    h1 {
        font-size: 1.8rem;
    }

    p {
        font-size: 1rem;
        margin-bottom: 30px;
    }

    .upload-box {
        padding: 30px 20px;
    }

    .select-btn {
        padding: 14px 25px;
        font-size: 1rem;
    }
}