If you click on the icon that appears in the middle of your screen on the left side, a menu opens in which you can perform the following actions;

Increase and decrease the font size
Grayscale, all the content will be greyed out at different scales differentiating content
High contrast, the content they go to a high contrast mode, to differentiate content
Negative contrast, all of the content they happen to have a negative contrast helping to differentiate sections
Light background transforms all over the web and puts on a white background colour to the same.
underline links, underlines all the links available in the web
Readable source, transforms the sources of the site to a readable source
Reset, reset all values to default on the web.