[Solved]-facing lots of trouble while installing semantic UI in react project-Reactjs

You missed a css processor in Webpack config:

      {
        // Preprocess our own .css files
        // This is the place to add your own loaders (e.g. sass/less etc.)
        // for a list of loaders, see https://webpack.js.org/loaders/#styling
        test: /\.css$/,
        exclude: /node_modules/,
        use: ['style-loader', 'css-loader'],
      },