Which magic CSS causes the difference of text-vertical-align between <button> and ?

Question

I found that the text inside of is automatically vertically centered, while text inside of

is top aligned.

I tri

Answer 1

If you look at Chrome source code you can kind of see how it works, at least for Chrome. It seems there's an anonymous flex box created with a specific style applied. It's not that straightforward — at least not for me — but still, you can deduce what style is applied to this anonymous element. You can see here: https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/layout/LayoutButton.cpp?sq=package:chromium

The interesting part:

void LayoutButton::updateAnonymousChildStyle(const LayoutObject& child,
                                             ComputedStyle& childStyle) const {
  ASSERT(!m_inner || &child == m_inner);

  childStyle.setFlexGrow(1.0f);
  // min-width: 0; is needed for correct shrinking.
  childStyle.setMinWidth(Length(0, Fixed));
  // Use margin:auto instead of align-items:center to get safe centering, i.e.
  // when the content overflows, treat it the same as align-items: flex-start.
  childStyle.setMarginTop(Length());
  childStyle.setMarginBottom(Length());
  childStyle.setFlexDirection(style()->flexDirection());
  childStyle.setJustifyContent(style()->justifyContent());
  childStyle.setFlexWrap(style()->flexWrap());
  // TODO (lajava): An anonymous box must not be used to resolve children's auto
  // values.
  childStyle.setAlignItems(style()->alignItems());
  childStyle.setAlignContent(style()->alignContent());
}

This gives something like this :

div span {
  display: flex;
  text-align: center; 
  min-width: 0px;
  flex-grow: 1;
  justify-content: center;
  cursor: default;
  margin: 0 auto;
  height: 100%;
  align-items: center;
  align-content: center;
}

Then you just need to wrap the div content in that span and apply the style. All these rules are probably not all necessary or accurate but the result seems ok:

div,
button {
  width: 4em;
  height: 4em;
  background-color: red;
  padding: 0;
  border: 0;
  margin: 1em;
  font-size: 1em;
  font-family: Arial;
  float: left;
}
div span {
  display: flex;
  text-align: center;
  min-width: 0px;
  flex-grow: 1;
  justify-content: center;
  cursor: default;
  margin: 0 auto;
  width: 100%;
  height: 100%;
  align-items: center;
  align-content: center;
}

text text

text text

text text text text

text text text text

text text text text text text

text text text text text text