Title Page with Operator Selection

So Many Numbers can now filter operators. For instance, you can play a game with:

• Addition/subtraction only
• Multiplication/division only
• Just addition
• Just multiplication
• etc.

To filter operators, add the query string ?mode= to the end of the game URL. Then type:

• a for add
• s for subtract
• m for multiply
• d for divide

A game with addition/subtraction would have the link:

https://so-many-numbers.github.io/game/?mode=as

A game with subtraction, multiplication, and division would have the link:

https://so-many-numbers.github.io/game/?mode=smd

By default (missing/invalid query string), the game will use all four operators.

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We need to add operator selectors to the game's title page. To achieve this:

• The title page should include +, -, x, and ÷ buttons.
  • Optionally include preset modes like +-, x÷, and +-x÷.
• When the user selects an operator, that button color should change to something distinct.
• Based on the operators selected, the START button's link should change to the corresponding query string.

Ideally (but not necessary):

• Don't show the START button until the user selects an operator.
• Scale the font size to fit each screen using viewport units.

I look forward to seeing what you got!