refactor: split monolithic App.css into feature-based co-located CSS files

src/components/common/FileImportModal.css

@@ -0,0 +1,161 @@
+/* File Import Modal */
+.file-import-overlay {
+  position: fixed;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  background-color: rgba(0, 0, 0, 0.7);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 10001;
+  backdrop-filter: blur(2px);
+}
+
+.file-import-modal {
+  background-color: #2d2d2d;
+  border: 1px solid #3a3a3a;
+  border-radius: 8px;
+  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.5);
+  width: 90%;
+  max-width: 500px;
+  max-height: 80vh;
+  overflow: hidden;
+  animation: fileImportFadeIn 0.2s ease-out;
+}
+
+@keyframes fileImportFadeIn {
+  from {
+    opacity: 0;
+    transform: scale(0.95) translateY(-10px);
+  }
+  to {
+    opacity: 1;
+    transform: scale(1) translateY(0);
+  }
+}
+
+.file-import-header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: 20px;
+  border-bottom: 1px solid #3a3a3a;
+  background-color: #252525;
+}
+
+.file-import-title {
+  color: #e0e0e0;
+  font-size: 18px;
+  font-weight: 600;
+  margin: 0;
+}
+
+.file-import-close-btn {
+  background: transparent;
+  border: none;
+  color: #b0b0b0;
+  cursor: pointer;
+  padding: 8px;
+  border-radius: 4px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  font-size: 16px;
+  transition: all 0.2s ease;
+}
+
+.file-import-close-btn:hover {
+  background-color: #3a3a3a;
+  color: #e0e0e0;
+}
+
+.file-import-drop-zone {
+  padding: 40px 20px;
+  margin: 20px;
+  border: 2px dashed #555;
+  border-radius: 8px;
+  background-color: #1e1e1e;
+  transition: all 0.3s ease;
+  cursor: pointer;
+}
+
+.file-import-drop-zone:hover {
+  border-color: #7b68ee;
+  background-color: rgba(123, 104, 238, 0.05);
+}
+
+.file-import-drop-zone.drag-over {
+  border-color: #7b68ee;
+  background-color: rgba(123, 104, 238, 0.1);
+  transform: scale(1.02);
+}
+
+.file-import-drop-content {
+  text-align: center;
+  color: #e0e0e0;
+}
+
+.file-import-icon {
+  font-size: 48px;
+  margin-bottom: 16px;
+  opacity: 0.7;
+}
+
+.file-import-description {
+  font-size: 18px;
+  font-weight: 500;
+  margin: 0 0 8px 0;
+  color: #e0e0e0;
+}
+
+.file-import-formats {
+  font-size: 14px;
+  color: #b0b0b0;
+  margin: 0 0 24px 0;
+}
+
+.file-import-divider {
+  position: relative;
+  margin: 24px 0;
+  text-align: center;
+}
+
+.file-import-divider::before {
+  content: '';
+  position: absolute;
+  top: 0;
+  left: 0;
+  right: 0;
+  height: 1px;
+  background-color: #3a3a3a;
+}
+
+.file-import-divider span {
+  background-color: #1e1e1e;
+  padding: 0 12px;
+  color: #888;
+  font-size: 12px;
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+}
+
+.file-import-browse-btn {
+  display: inline-block;
+  background-color: #5a9fd4;
+  color: #fff;
+  padding: 12px 24px;
+  border-radius: 6px;
+  font-size: 14px;
+  font-weight: 500;
+  cursor: pointer;
+  transition: all 0.2s ease;
+  border: none;
+}
+
+.file-import-browse-btn:hover {
+  background-color: #4a8fc4;
+  transform: translateY(-1px);
+  box-shadow: 0 4px 12px rgba(90, 159, 212, 0.3);
+}

src/components/common/FileImportModal.tsx

@@ -1,4 +1,5 @@
 import React, { useCallback, useState } from 'react';
+import './FileImportModal.css';
 import { FaTimes } from 'react-icons/fa';
 
 interface FileImportModalProps {

src/components/common/LoadingOverlay.css

@@ -0,0 +1,36 @@
+/* Global Loading Overlay */
+.global-loading-overlay {
+  position: fixed;
+  inset: 0;
+  background-color: rgba(0, 0, 0, 0.4);
+  z-index: 20000;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  pointer-events: all; /* block interactions */
+}
+
+.global-loading-content {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 10px;
+}
+
+.global-loading-spinner {
+  width: 40px;
+  height: 40px;
+  border: 4px solid rgba(255, 255, 255, 0.25);
+  border-top-color: #ffffff;
+  border-radius: 50%;
+  animation: globalSpinner 1s linear infinite;
+}
+
+.global-loading-text {
+  color: #e0e0e0;
+  font-size: 14px;
+}
+
+@keyframes globalSpinner {
+  to { transform: rotate(360deg); }
+}

src/components/common/LoadingOverlay.tsx

@@ -1,4 +1,5 @@
 import React from 'react';
+import './LoadingOverlay.css';
 
 interface LoadingOverlayProps {
   visible: boolean;