fix(NcModal): apply box sizing to modal content

[Antreesy]

☑️ Resolves

• Fix box-sizing property for nested components:
  • If NcModal is mounted inside of #content-vue element, as all other components, it inherits style from NcContent (see here
    33f4af3)
  • But by default, NcModal is mounted in body element, where styles are not overwritten, and all element apart from <table>, <select>, <button> and <input> elements have `box-sizing: content-box by default
  • This will affect <div class="modal-container">, <div class="modal-container__content">, and all that goes to <slot />

🖼️ Screenshots

🏚️ Before	🏡 After

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable

[ShGKme]

I wonder if this counts as a breaking change.

Probably may break some modals that had content with styles for default border-box...

But I'd make this change, having different styles depending on mount point isn't good.

And +1 thing to think about global box-sizing: border-box; (#4956 👀)

[susnux]

Probably may break some modals that had content with styles for default border-box...

I think every more complex modal will be broken as most of them are mounted to the body. So this needs to be considered.

[Antreesy]

Maybe we put in on the next branch, as we should prepare a migration guide for it anyway? I'm assuming, that more or less complex modals including it already, so with moving to Vue 3 it wouldn't be a huge task to check styles

[ShGKme]

@skjnldsv Does your approval mean we may not consider it as a breaking change and merge into v8? 😀

[skjnldsv]

@skjnldsv Does your approval mean we may not consider it as a breaking change and merge into v8? 😀

Nah, should be for v9 then

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