Inner working

This is how Mantine implements and ships <Button>

sourcecode (unbuilt)

html elements structure

• the innermost span contains only text
• the intermediate inner span contain icons and the innermost span
• the root contains the inner span, and may probably replace it on loading state.

button // root
	span // inner
		span // label
			text
		span
	span
button

layer terminology and empty classes

root // mantine-Button-root
	inner // mantine-Button-inner
		label // mantine-Button-label
			text
		label
	inner
root

mantine implementation classes and empty classes

<button class="m-77c9d27d mantine-Button-root .." type="button">
    {" "}
    // root
    <span class="m-80f1301b mantine-Button-inner">
        {" "}
        // inner
        <span class="m-811560b9 mantine-Button-label"> // label Save</span>
    </span>
</button>

class analysis

All those classes appear on root, which here is the <button> element.

m-87cf2631				// Mantine implementation class, (UnstyledButton)
m-77c9d27d				// Mantine implementation class, (Button)

mantine-UnstyledButton-root	// empty class
mantine-Button-root					// empty class

mantine-active
// Mantine implementation class
/*
mantine-active:active {
    transform: translateY(calc(.0625rem * var(--mantine-scale)));
}
*/
mantine-focus-auto	// allows :focus-visible

mantine source style for Button's root:

Mantine's implementation of root:

.root {
    --button-height-xs: 30px;
    --button-height-sm: 36px;
    --button-height-md: 42px;
    --button-height-lg: 50px;
    --button-height-xl: 60px;

    --button-height-compact-xs: 22px;
    --button-height-compact-sm: 26px;
    --button-height-compact-md: 30px;
    --button-height-compact-lg: 34px;
    --button-height-compact-xl: 40px;

    --button-padding-x-xs: 14px;
    --button-padding-x-sm: 18px;
    --button-padding-x-md: 22px;
    --button-padding-x-lg: 26px;
    --button-padding-x-xl: 32px;

    --button-padding-x-compact-xs: 7px;
    --button-padding-x-compact-sm: 8px;
    --button-padding-x-compact-md: 10px;
    --button-padding-x-compact-lg: 12px;
    --button-padding-x-compact-xl: 14px;

    --button-height: var(--button-height-sm);
    --button-padding-x: var(--button-padding-x-sm);
    --button-color: var(--mantine-color-white);

    user-select: none;
    font-weight: 600;
    position: relative;
    line-height: 1;
    text-align: center;
    overflow: hidden;

    width: auto;
    cursor: pointer;
    display: inline-block;
    border-radius: var(--button-radius, var(--mantine-radius-default));
    font-size: var(--button-fz, var(--mantine-font-size-sm));
    background: var(--button-bg, var(--mantine-primary-color-filled));
    border: var(--button-bd, rem(1px) solid transparent);
    color: var(--button-color, var(--mantine-color-white));
    height: var(--button-height, var(--button-height-sm));
    padding-inline: var(--button-padding-x, var(--button-padding-x-sm));
    vertical-align: middle;

    &:where([data-block]) {
        display: block;
        width: 100%;
    }

    &:where([data-with-left-section]) {
        padding-inline-start: calc(var(--button-padding-x) / 1.5);
    }

    &:where([data-with-right-section]) {
        padding-inline-end: calc(var(--button-padding-x) / 1.5);
    }

    &:where(:disabled:not([data-loading]), [data-disabled]:not([data-loading])) {
        cursor: not-allowed;
        border: 1px solid transparent;
        transform: none;

        @mixin where-light {
            color: var(--mantine-color-gray-5);
            background: var(--mantine-color-gray-1);
        }

        @mixin where-dark {
            color: var(--mantine-color-dark-3);
            background: var(--mantine-color-dark-6);
        }
    }

    &::before {
        content: "";
        pointer-events: none;
        position: absolute;
        inset: -1px;
        border-radius: var(--button-radius, var(--mantine-radius-default));
        transform: translateY(-100%);
        opacity: 0;
        filter: blur(12px);
        transition: transform 150ms ease, opacity 100ms ease;

        @mixin where-light {
            background-color: rgba(255, 255, 255, 0.15);
        }

        @mixin where-dark {
            background-color: rgba(0, 0, 0, 0.15);
        }
    }

    &:where([data-loading]) {
        cursor: not-allowed;
        transform: none;

        &::before {
            transform: translateY(0);
            opacity: 1;
        }

        & .inner {
            opacity: 0;
            transform: translateY(100%);
        }
    }

    @mixin hover {
        &:where(:not([data-loading], :disabled, [data-disabled])) {
            background-color: var(--button-hover, var(--mantine-primary-color-filled-hover));
            color: var(--button-hover-color, var(--button-color));
        }
    }
}

style shipped on npm

the style is mostly the same. It is probably processed by PostCSS. It does not use CSS nesting.

.m_77c9d27d {
    /* zip, the code is the same */
    /* ... */
    /* ... */
    /* ... */
    /* ... */
    /* ... */

  .m_77c9d27d:where([data-block]) {
    display: block;
    width: 100%;
  }

  .m_77c9d27d:where([data-with-left-section]) {
    padding-inline-start: calc(var(--button-padding-x) / 1.5);
  }

  .m_77c9d27d:where([data-with-right-section]) {
    padding-inline-end: calc(var(--button-padding-x) / 1.5);
  }

  .m_77c9d27d:where(:disabled:not([data-loading]), [data-disabled]:not([data-loading])) {
    cursor: not-allowed;
    border: 1px solid transparent;
    transform: none;
  }

  :where([data-mantine-color-scheme='light']) .m_77c9d27d:where(:disabled:not([data-loading]), [data-disabled]:not([data-loading])) {
      color: var(--mantine-color-gray-5);
      background: var(--mantine-color-gray-1);
}

  :where([data-mantine-color-scheme='dark']) .m_77c9d27d:where(:disabled:not([data-loading]), [data-disabled]:not([data-loading])) {
      color: var(--mantine-color-dark-3);
      background: var(--mantine-color-dark-6);
}

  .m_77c9d27d::before {
    content: '';
    pointer-events: none;
    position: absolute;
    inset: -1px;
    border-radius: var(--button-radius, var(--mantine-radius-default));
    transform: translateY(-100%);
    opacity: 0;
    filter: blur(12px);
    transition:
      transform 150ms ease,
      opacity 100ms ease;
  }

  :where([data-mantine-color-scheme='light']) .m_77c9d27d::before {
      background-color: rgba(255, 255, 255, 0.15);
}

  :where([data-mantine-color-scheme='dark']) .m_77c9d27d::before {
      background-color: rgba(0, 0, 0, 0.15);
}

  .m_77c9d27d:where([data-loading]) {
    cursor: not-allowed;
    transform: none;
  }

  .m_77c9d27d:where([data-loading])::before {
      transform: translateY(0);
      opacity: 1;
    }

  .m_77c9d27d:where([data-loading]) .m_80f1301b {
      opacity: 0;
      transform: translateY(100%);
    }

  @media (hover: hover) {
    .m_77c9d27d:hover:where(:not([data-loading], :disabled, [data-disabled])) {
      background-color: var(--button-hover, var(--mantine-primary-color-filled-hover));
      color: var(--button-hover-color, var(--button-color));
    }
}

  @media (hover: none) {
    .m_77c9d27d:active:where(:not([data-loading], :disabled, [data-disabled])) {
      background-color: var(--button-hover, var(--mantine-primary-color-filled-hover));
      color: var(--button-hover-color, var(--button-color));
    }
}

It is then processed even more and merged to a gigantic 232kb stylesheet, shipped on npm too, the one we import from our app.