to add rules wherever you like, use the rule mark: add Plot.ruleY([0]) next to the Plot.dot() mark you already have. https://observablehq.com/plot/marks/rule you can also enable the grids by adding "grid: true" property inside y: {} encoding setting to solve colors, go to this cheat-sheet and copy the solution for diverging color scheme (i tried and it worked), you would need to set "fill" encoding to "gender diff" for your "dot" mark. https://observablehq.com/@observablehq/plot-colors-cheatsheet country labels would be good to have: how about another mark "text" with the same x and y and text encoding set to countries? see examples here https://observablehq.com/plot/marks/text

the # column is only added as a presentation layer in the table, it's not actually in data you can hide it if you press kebab menu on the column

i fixed the search-highlight, see text above in comments

i wanted to add a year slider, but the data has only one year. please first add data for other years :) then add a slider like below and see if you can use "filter" like in examples here https://observablehq.com/plot/transforms/filter