You can import Katex. I got here via https://stackoverflow.com/a/65540803/5599595. Running in shinylive

from shiny.express import ui
from shiny import render

with ui.tags.head():
    # Link KaTeX CSS
    ui.tags.link(
        rel="stylesheet",
        href="https://cdn.jsdelivr.net/npm/[email protected]/dist/katex.min.css"
    ),
    ui.tags.script(src="https://cdn.jsdelivr.net/npm/[email protected]/dist/katex.min.js"),
    ui.tags.script(src="https://cdn.jsdelivr.net/npm/[email protected]/dist/contrib/auto-render.min.js"),
    ui.tags.script("""
        document.addEventListener('DOMContentLoaded', function() {
            renderMathInElement(document.body);
        });
    """)

with ui.card():
    ui.p("Here's a quadratic formula: \\[x = \\frac{-b \\pm \\sqrt{b^2 - 4ac}}{2a}\\]")
    ui.p("And an inline equation: \\(E = mc^2\\)")
    ui.p("\\[3 \\times 3+3-3 \\]")