“Master” is a strong word, but when I have to build applications it’s PHP in the back and JS up front. Specifically, Laravel implementations with whatever on top.
I’m extremely proficient with templating languages that eventually turn into HTML (nunjucks, antlers, blade, handlebars, webc, vue) and CSS (SCSS, LESS). A ton of my work winds up being on Static Site Generators and the unholy abomination that is at-scale Email development.