It is a unicode character: β–Ά = ▶

http://www.fileformat.info/info/unicode/char/25b6/index.htm

See: What characters can be used for up/down triangle (arrow without stem) for display in HTML?

Answer from Diodeus - James MacFarlane on Stack Overflow
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Toptal
toptal.com β€Ί designers β€Ί htmlarrows β€Ί arrows
HTML Arrow Symbols, Entities and Codes β€” Toptal Designers
Easily find HTML arrow symbols, entities, characters and codes with ASCII, HEX, CSS and Unicode values; including right arrow, left arrow, up and down arrows.
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HTML Symbols
htmlsymbols.net β€Ί arrows
Arrows HTML Symbols List: Copy, Unicode & Code Reference
Find and copy 296 Arrows HTML symbols and special characters with Unicode, HTML, HEX & CSS code. Fast search and use in your web pages.
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Steemit
steemit.com β€Ί steemhunt β€Ί @smyle β€Ί html-arrows-delightful-tool-for-html-symbols-entities-and-ascii-codes
HTML Arrows - Delightful tool for HTML Symbols, Entities and ASCII Codes β€” Steemit
June 7, 2019 - This site is loaded with HTML arrow symbols, arrow entities, Unicode and ASCII arrow character codes that you can use on your web project.
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FSymbols
fsymbols.com β€Ί signs β€Ί arrow
β†“β†³βžœβ‡’βž€πŸΉβž΅πŸ’˜ Arrow (copy and paste emoji text symbol)
Copy and paste + Find how to text arrow signs ➟ ➑ ➒ ➣ ➀ βž₯ ➦ ➧ ➨ ➚ ➘ βž™ βž› ➜ ➝ ➞ ➸ ♐ ➲ ➳ ➳ ➴ ➡ ➢ ➷ ➸ ➹ ➺ β†– β†— β†˜ ↙ β†š ↛ ⏎ directly from your keyboard. You can put them in Facebook, Youtube or Instagram.
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SYMBL
symbl.cc β€Ί homepage β€Ί symbol collections β€Ί arrow symbols
Arrow symbols ‭→ β–Ά βž”β€¬ Copy and Paste emoticon (β—•β€Ώβ—•) SYMBL
1 day ago - Looking for Arrow Symbols? Check these out: ‭→ β–Ά βž” ➜ βžβ€¬β€¬. Copy & paste up, down, right and left arrow characters and emoticons for any text. Discover more glyphs and emojis at (β—•β€Ώβ—•) SYMBL!
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Arrow Symbol
arrowsymbol.com
Arrow Symbols β†— Easy Copy Paste
List of arrow symbols with unicode, html code and graphical symbol.
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Keynote Support
keynotesupport.com β€Ί internet β€Ί special-characters-arrows.shtml
ALT, HTML, Unicode, Hex, and CSS Codes for Arrows
Unicode, ALT codes, HTML codes, and HTML Entities for arrows: up, down, left, right, and different styles
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W3Schools
w3schools.com β€Ί charsets β€Ί ref_utf_misc_symb_arr.asp
Unicode Miscellaneous Symbols and Arrows
Currency Symbols Letterlike Symbols Number Forms Enclosed Alpha Enclosed Ideographic Box Drawings Geometric Shapes Misc Symbols Dingbats Ornamental Dingbats UTF-8 Arrows
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Toptal
toptal.com β€Ί designers β€Ί htmlarrows β€Ί symbols
HTML Symbols, Entities and Codes β€” Toptal Designers
Easily find HTML symbols, entities, characters and codes with ASCII, HEX, CSS and Unicode values; including copyright sign, trademark sign and at symbol.
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Remix Icon
remixicon.com
Remix Icon - Open source icon library
Remix Icon is a set of open source neutral style system symbols elaborately crafted for designers and developers. All of the icons are free to use for both personal and commercial.
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Font Awesome
fontawesome.com β€Ί v4 β€Ί cheatsheet
Font Awesome Cheatsheet
ο‚« fa-arrow-circle-down []  fa-arrow-circle-left [] ο€š fa-arrow-circle-o-down [] 4.0  fa-arrow-circle-o-left [] 4.0 ο†Ž fa-arrow-circle-o-right [] ο€› fa-arrow-circle-o-up [] ο‚© fa-arrow-circle-right [] ο‚ͺ fa-arrow-circle-up []  fa-arrow-down []  fa-arrow-left []  fa-arrow-right []  fa-arrow-up []  fa-arrows [] ο‚² fa-arrows-alt []  fa-arrows-h []  fa-arrows-v [] 4.6  fa-asl-interpreting (alias) [] 4.6  fa-assistive-listeni
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W3Schools
w3schools.com β€Ί charsets β€Ί ref_utf_arrows_supp_a.asp
HTML Unicode Supplemental Arrows A
Well organized and easy to understand Web building tutorials with lots of examples of how to use HTML, CSS, JavaScript, SQL, Python, PHP, Bootstrap, Java, XML and more.
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Reddit
reddit.com β€Ί r/html β€Ί help with unicode arrows
r/HTML on Reddit: Help with unicode Arrows
September 10, 2018 -

Does anyone know how to change the + and - to those solid triangles pointing > and V that are commonly used in buttons/collapsible?

.bArticle:after { content: '\02795'; /* Unicode character for "plus" sign (+) / font-size: 13px; color: black; float: right; margin-left: 5px; margin-bottom: 5px; }

.active:after { content: "\2796"; / Unicode character for "minus" sign (-) */

Sorry if i didn't format very well, I know I should change the content: "____" but I don't know what to change them to. I tried a bunch of random unicode lines I found on google but none of them seem to do the trick.

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APIVoid
apivoid.com β€Ί tools β€Ί html-arrows-list
HTML Arrows List – Unicode, Hex & HTML Codes | APIVoid
View all HTML arrow symbols with Unicode, hex, and HTML codes. Copy and use arrows for websites, design, and emails. Ideal for developers and designers.