Try clean cache of browser and prestashop.
In Chrome
On your computer, open Chrome.
At the top right, click More .
Click More tools Clear browsing data.
At the top, choose a time range. To delete everything, select All time.
Next to "Cookies and other site data" and "Cached images and files," check the boxes.
Click Clear data.
Clean cache prestashop :
You can try disable Smart cache for CSS too.