Button: remove margin from default style

[mozart77]

Describe the feature you would like to see added

Hi. I think margin set to 0 to buttons is bad idea because it makes you use !important rules to margin these elements.

BaseComponent.vue:9:

const buttonStyles = `
.p-button {
    margin: 0;
    display: inline-flex;
    cursor: pointer;
    user-select: none;
    align-items: center;
    vertical-align: bottom;
    text-align: center;
    overflow: hidden;
    position: relative;
} 

Is your feature request related to a problem?

No response

Describe the solution you'd like

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Describe alternatives you have considered

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Additional context

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