[suggestion] expose font family variables for custom themes

[KagamiChan]

#1059 provides an example of overriding default fonts, but it turns out the snippet is insufficient for monospace because there're more selectors that has tailwindcss font-mono applied

giscus/styles/base.css

Lines 305 to 310 in d85cb25

	.commit-tease-sha {
	@apply font-mono;
	font-size: 90%;
	color: var(--color-fg-default, var(--color-text-primary));
	}

giscus/styles/base.css

Lines 356 to 361 in d85cb25

	.blob-num {
	/* stylelint-disable-next-line max-line-length */
	@apply w-[1%] min-w-[50px] px-[10px] font-mono text-xs leading-5 text-right whitespace-nowrap align-top cursor-pointer select-none;
	color: var(--color-fg-subtle, var(--color-diff-blob-num-text));
	}

giscus/styles/base.css

Lines 371 to 375 in d85cb25

	.blob-code-inner {
	@apply overflow-visible font-mono text-xs whitespace-pre;
	word-wrap: normal;
	}

giscus/styles/base.css

Lines 882 to 884 in d85cb25

	.gsc-is-fixed-width {
	@apply font-mono;
	}

giscus/styles/globals.css

Lines 188 to 190 in d85cb25

	.markdown .footnotes .data-footnote-backref .g-emoji {
	font-family: monospace;
	}

Could we unify all these places and provide a font family css variable so that customizing font family could be easier? I can implement if this feature is agreed,