HTML character entity references for maximize and minimize

Unicode's Miscellaneous Symbols And Pictographs provides some window button glyphs:

🗕︎ 🗖︎ 🗙︎
🗕︎ 🗖︎ 🗙︎

🗕︎ 🗗︎ 🗙︎
🗕︎ 🗗︎ 🗙︎

However, these will not display well on all platforms. You should use SVG if you can.
(Or, include and use a font that specifically defines these.)

The ︎ is to prevent display as emoji. It's not guaranteed tho, and for instance my phone doesn't support it and will show emoji for all four of these glyphs.

You can use − for minimize(−) and + for maximize(+) like × for ×

Well, for minimize, we have pure _ or _ and for maximize □. If you are expecting a fancy option for minimize, you can also use ⊟

Demo

× _ □

The above will output × _ □

For more information, you can refer to Character Entity Reference Chart.