It override my stylus theme, I tried .tooltipDiv {background-color: #0f1b1b !important;font-size: 18px !important;} and it only work for less than a second.

I want it more readable for old user.

Edit:MB it's Dark Background and Light Text fault, I need to set it to css-only to not override other addon style

quite good add-on.
this may replace the good "Wiktionary and Google Translate" add-on.

It's very good. Shows definitions instantly.