```python
from fastapi import FastAPI
from starlette.middleware.cors import CORSMiddleware

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

app = FastAPI()

origins = [
    "http://localhost",
    "http://localhost:8000",
]

app.add_middleware(
    CORSMiddleware,
    allow_origins=origins,
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

SQLALCHEMY_DATABASE_URL = "sqlite:///./blog_app.db"
engine = create_engine(SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False})
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
Base = declarative_base()

from . import models, routes

app.include_router(routes.router)

@app.get("/")
async def root():
    return {"message": "Welcome to the Blog App!"}
```


1. Imports necessary FastAPI, middleware, and SQLAlchemy modules.
2. Creates a FastAPI app instance.
3. Configures CORS middleware to allow cross-origin requests from specified origins.
4. Sets up the SQLite database connection using SQLAlchemy.
5. Imports models and routes after the database configuration to avoid circular imports.
6. Includes the routes from the `routes` module.


You can run this FastAPI app using the `uvicorn` command:

```bash
uvicorn main:app --reload
```

This will start the development server and automatically reload it when you make changes to the code.