This is usually the result of a local browser setting that can be solved with toggling the size to 100% and relaunching the browser session.
If that doesn't resolve the issue, you can also try resetting your browser scale. Each browser does this somewhat differently, in Chrome for example, you can reset your scale in Advanced settings:
> Click the menu icon next to the address bar (three vertical dots, when scrolled over "Customize and Control Google Chrome" will appear
> Select Settings from the drop-down menu
> Scroll to the bottom of the Settings page and click the Advanced link
> Scroll to the bottom of the expanded page and click the Reset button.
> Click the Reset button in the pop-up window.
Resetting may log you out of other active sessions or programs that you have open so please close and save your work first.