You can make text and images larger so they’re easier to view.
Make the webpage content larger: Choose View > Zoom In, press Command–Plus Sign (+), or pinch open on a trackpad or mouse that supports gestures. To make only text larger, choose View > Zoom Text Only before you zoom in.
Set a minimum font size for webpages: Choose Safari > Preferences, click Advanced, then select “Never use font sizes smaller than.” Click the pop-up menu, then choose the minimum font size you want.
Expand to full-screen view: Click the green full-screen button 
in the top-left corner of the browser window, or press Control-Command-F. To stop using the app full screen, move the pointer to the top-left corner of the screen, then click the green full-screen button again, or press Control-Command-F.
Use Safari in Split View: Click and hold the green full-screen button in the top-left corner of the browser window, drag the Safari window to the side of the screen you want, then release the button. Select an app that supports Split View on the other half of the screen.