You can change the default theme using the menu icon in the right hand corner. We have a couple of themes preset, you can try implementing your own color scheme by selecting the "Settings" option.
The detailed descriptions on DDG and Google are both exactly the same size, 13px. I think the people complaining about these visual issues are imagining things.
Font size isn't exactly comparable across different font families. In the case of DDG they are using DDG_ProximaNova, while in the case of Google they are using Arial.
Arial is much easier to read on Chrome for Windows over DDG_ProximaNova.
I also just noticed that we can change the font on the settings page, just feel like it shouldn't be necessary.