Portuguese term
seriedade não tira leveza
Proposed translations
Brazil
Video game localization and marketing
Native in: Portuguese (Variant: Brazilian)
Works in: English to Portuguese, Portuguese to English
it is possible to be both serious and lighthearted at the same time
I am assuming you've translated "séria" to "serious".
Will do!
Native in: Portuguese (Variant: European/Portugal) 
Works in: English to Portuguese, French to Portuguese, German to Portuguese, and 1 more.
seriousness and lightness
https://www.google.com/search?q="seriousness and lightness"&...
“Do what you love, and do it with both seriousness and lightness” -Elizabeth Gilbert
Shot in a straightforward style, the film strikes an unusual balance between seriousness and lightness.'
Brazil
32 years engineering/law/contracts
Native in: English (Variant: US) , Portuguese (Variant: Brazilian) 
Works in: English to Portuguese, Portuguese to English
seriousness does not suppress/eliminate/kill lighness
Bachelor of Pharmacy
Native in: Portuguese (Variant: Brazilian)
Works in: English to Portuguese, Slovenian to Portuguese, Portuguese to English, and 1 more.
serious can be light
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Note added at 6 days (2020-11-24 09:31:00 GMT)
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Outra opção seria: "fortunately, serious doesn't need to be stuffy"
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